What were the international politics of the years from 1848 to the 1870s about? Traditional western historiography had very little doubt: it was about the creation of a Europe of nation-states. 
1848 was 'the springtime of peoples; assertion of nationality, or rather rival nationalities  'nation-making (coined by Walter Bagehot). 
The  revolutions [of Czechs, Croats, Danes, et al.] failed, but the European politics of the next twenty-five yers were dominated by the same aspirations. 
In the extreme west, as in the extreme south-east, of Europe the national problem obstruded itself. The Fenians of Ireland raised it in the form of radical insurrection, backed by the millions of their countrymen driven by famine and hatred of Britain to the United States. The endemic crisis of the multi-national Ottoman Empire took the form of revolts of various Christian peoples it had so long ruled in the Balkans 
The nation was taken for granted. As Baghot put it: We cannot imagine those to whom it is a difficulty: 'we know what is when you do not ask us, but we cannot very quickly explain or define it, and few thought they needed to. Surely the Englishman knew what being English was, the Frenchman, German, Italian or Russian had no doubt about their collective identity? Perhaps not, but in the age of nation-building this was believed to imply the logical necessary, as we as desirable transformation of nations into sovereign nation-states, with a coherent territory defined by the area settled by the members of a nation, which was in turn defined by its past history, common culture, it s ethnic composition and, increasingly, its language. But there is nothing logical about this implication. If the existence of differing groups of men, distinguishing themselves from other groups by a variety of criteria is both undeniable and as old as history, the fact that they imply what the nineteenth century regarded as nationhood is not. Still less so is the fact that they are organised in territorial states of the nineteenth-century kind, let alone states coinciding with nations. These were relatively recent phenomena, though some older territorial states - England, France, Spain, Portugal and perhaps even Russia - could have been defined as nation-states without obvious absurdity. Even as a general programme, the aspiration to form nation-states out of non-nation-states was a product of the French Revolution. We must therefore distinguish rather clearly between the formation of nations and nationalism, in so far as this took place during our period, and the creation of nation-states. 
[.] For Europe, let alone the rest of the world, was evidently divided into nations about whose states or aspirations to found states there was, rightly or wrongly, little doubt, and those about which there was a considerable  amount of uncertainty. The safest guide to the first was political fact, institutional history or the cultural history of the literate. 
The historic criterion of nationhood [.] implied the decisive importance of the institutions and culture of the ruling classes or educated elites, supposing them to be identified, or not too obviously incompatible with, those of the common people. But the ideological argument for nationalism was very different and much more radical, democratic and revolutionary. It rested on the fact that, whatever history or culture said, the Irish were Irish, not English, the Czechs Czech, not German, the Finns were not Russian, and no people ought to be exploited and ruled by another. Historic arguments might be found or invented to back this claim - they can always be discovered - but essentially the Czech movement did not rest on the claim to restore the Crown of St Wenceslas, not the Irish on the Repeal of the Union of 1801. The basis of this sense of separateness was not necessarily ethnic, in the sense of readily identifiable difference in physical appearance, or even linguistic. During our period the movements of the Irish (most of whom already spoke English), the Norwegians (whose literate language was not very distinct from Danish) or the Finns (whose nationalists were both Swedish- and Finnish-speaking) did not make a fundamentally linguistic case for themselves. If it was cultural, it rested not on high culture, of which several of the peoples concerned as yet had little,  but rather on the oral culture - songs, ballads, epics, &c., the customs and way of life of the folk - the common people, i.e., for practical purposes the peasantry. The first stage of national revival was invariably one of collecting, recovering or acquiring pride in this folk heritage. But in this it was not political. Those who pioneered it were, as often as not, cultured members of the foreign ruling class or elite, such as the German Lutheran pastors or intellectually minded gentlemen in the Baltic who collected the folklore and antiquities of the Latvian or Estonian peasantry. The Irish were not nationalists because they believed in leprechauns. (pp.106-07.)
The [...] typical un-historical or semi-historical nation was also a small nation, and this faced nineteenth-century nationalism with a dilemma [...] For the champions of the nation-state assumed not only that it must be national, but also that it must be progressive, i.e., capable of developing a viable economy, technology, state organisation and military force, i.e., that it must be at least moderately large. it was to be, in fact, the natural unit of the development of the modern, liberal, progressive and de facto bourgeois society. Unification as much as independence was its principal, and where no historic arguments of unification existed - as they did for example in Italy and Germany - it was, where feasible, formulated as a programme. 
The simplest argument for those who identified nation-states with progress was to deny the character of real nations to the small and backward peoples, or to argue that progress must reduce them to mere provincial idiosyncrasy within the larger real nations, or even lead to their actual disappearance by assimilation to some Kulturvolk. [108.]
There was a strong element of inegalitarianism and perhaps a stronger one of special pleading in such arguments. Some nations - the large, the advanced, the established, including the ideologists own - were destined by history to prevail or (if the ideologist preferred Darwinian phraseology) to be victors in the struggle for existence; others were not. Yet this must not be interpreted simply as a conspiracy of some nations to oppress others, though spokesmen of the unrecognised nations could hardly be blamed for thinking so. For the argument was directed as much against the  regional languages and cultures of the nation itself as against outsiders, and did not necessarily envisage their disappearance, but only their down-grading from the status of language to that of dialect. 
Faced with the nationalist aspirations of small peoples. the ideologists of a national Europe [.] had three choices: they could deny their legitimacy or their existence altogether, they could reduce them to movements for regional autonomy, and they could accept them as undeniable but unmanageable facts. The Germans tended to do the first with such people as the Slovenes, Hungarians with the Slovaks. Cavour and Mazzini took the second view about the Irish movement. Nothing is more paradoxical than their failure to fit into the nationalist pattern the one national movement about whose mass basis their could be no conceivable doubt. Politicians of all kinds were constrained  to take the third view of the Czechs, whose national movement, though not then envisaging total independence, could no longer be argued away after [the revolution of] 1848. Where possible, of course, they paid no attention to such movements at all. Hardly any foreigner bothered to note that several of the most old-established national states were in fact multinational (e.g., Britain, France and Spain), for the Welsh, Scots, the Bretons, the Catalans, &c., posed no international problem, and (with the possible exception of the Catalans) no significant problem to the domestic political of their own country. 
There was thus a fundamental difference between the movement to found nation-states and nationalism. The one was a programme to construct a political artefact claiming to be based on the other.  Nevertheless, whatever their nature and programme, movements representing the national idea grew and multiplied [...; 111]
Nor should be overlook the difference between old and new nationalisms, the former including only the historic nations not yet possessing their own states, but those who had long done so. How British did the British feel? No very, in spite of the virtual absence at this stage of any movements for Welsh and Scottish autonomy. There was English nationalism, but it was not shared by the smaller nations in the island. English emigrants to the United States were proud of their nationality, and therefore reluctant to become American citizens, but the Welsh and Scottish immigrants had no such loyalty. They could remain proudly Welsh and Scottish under American as under British citizenship, and naturalised themselves freely. How French did the members of even la grande nation feel? 
These were countries in which mass nationalism and patriotism could hardly be denied, and they demonstrate how unwise it is to take its universality and homogeneity for granted.
In most nations, especially the emergent ones, only myth and propaganda would have taken it for granted in the mid-nineteenth century. [For obvious reasons the most traditional, backward or poor sections of a people were the last to be involved in such movements: workers, servants and peasants, who followed the path traced by the educated elite. The phase of nationalism, which therefore normally came under the influence of organisations of the nationalist liberal-democratic middle strata - except when offset by independent  labour and socialist parties - was to some extent correlated with economic and political development. (pp.112-113)
[Development of mass nationalism]: For lack of a proper name for such activities, the Czech initially borrowed the term meeting for them from the Irish movement which they attempted to copy. Soon a suitably traditional name was devised by harking back to the Hussites of the fifteenth century, a natural example of Czech national militancy, the tabor. (p.113.)
This kind of mass nationalism was new, and quite distinct from the elite or middle-class nationalism of the Italian or German movement. (p.113.)
Irish Republican Brotherhood 
One such [proto-nationalist] movement, however, was unquestionably national: the Irish. The Irish Republican Brotherhood (Fenians), with its still surviving Irish Republican Army, was the lineal descendant of the secret revolutionary fraternities of the pre-1848 period, and the longest-lived organisation of its kind. Mass rural support for nationalist politicians was not in itself new, for the Irish combination of foreign conquest, poverty, oppression and a largely Anglo-Protestant landlord class imposed on an Irish-Catholic peasantry mobilised the least political. In the first-half of the century the leaders of these mass movements had belonged to the (small) Irish middle class and their aim - supported by the only effective national organisation, the church - had been a moderate accommodation with the English. The novelty of the Fenians, who first appeared as such in the late 1850s, was that they were entirely independent of the middleclass moderates, that their support came entirely from among the popular masses - even, in spite of the open hostility of the Church, parts of the peasantry - and that they were the first to put forward a programme of total independence from England, to be achieved by armed insurrection. In spite of their name, derived from the heroic mythology of ancient Ireland, their ideology was quite nontraditional, though its secular, even anti-clerical nationalism cannot conceal that for the mass of the Fenian Irish the criterion of nationality was (and still is) the Catholic faith. Their wholehearted concentration on an Irish Republic won by armed struggle replaced a social and economic, even a domestic political programme, and their heroic legend of rebel gunmen and martyrs has up to the present been too strong for those who wanted to formulate one. This is the Republican tradition which survives into the 1970s and has re-emerged in the Ulster civil war, in the Provisional IRA. The readiness of the Fenians to ally themselves with socialist revolutionaries, and of these to recognise the revolutionary character of Fenianism, should not encourage illusions about this. [Ftn.: Marx supported them strongly and was in correspondence with Fenian leaders.]
But neither should we underestimate the novelty, and the historic significance, of a movement whose financial support came from the masses of Irish labourers driven by famine and hatred of England to the United States, whose recruits came from Irish emigrant proletarians in America and England - there were hardly any industrial workers in what is now the Irish Republic - and from young peasants and farm-workers in the ancient strongholds of Irish agrarian terrorism; whose cadres were men such as these and the lowest strata of revolutionary urban white-collar workers, and whose leaders dedicated their lives to insurrection. It anticipates the revolutionary national movements of under-developed countries in the twentieth century. It lacked the core of socialist labour organisation, or perhaps merely the inspiration of a socialist ideology, which was to turn the combination of national liberation and social transformation into such a formidable force in this century. There was no socialism anywhere, let alone socialist organisation in Ireland, and the Fenians who were also social revolutionaries, notably Michael Davitt (1846-1906), succeeded merely in making explicit in the Land League the always implicit relation between mass nationalism and mass agrarian discontent; and even this not until after the end of our period, during the great Agrarian Depression of the late 1870s and 1880s. Fenianism was mass nationalism in the epoch of triumphant liberalism. It could do little except reject England and demand total independence through revolution for an oppressed people, hoping that somehow this would solve all problems of poverty and exploitation. It did not do even this very effectively, for in spite of the self-abnegation and heroism of the Fenians, their scattered insurrections (1867) and invasions (e.g. of Canada from the United States) were conducted with notable inefficiency, and their dramatic coups achieved, as is usual in such operations, little more than temporary publicity; occasionally bad publicity. They generated the force which was to win independence for most of Catholic Ireland but, since they generated nothing else, they left the future of that Ireland to the middle-class moderates, the rich farmers and small-town tradesmen of a small agrarian country who were to take over their heritage.
Though the Irish case was still unique, there is no denying that in our period nationalism increasingly became a mass force, at least in the countries populated by whites. Even though the Communist Manifesto was less unrealistic than is often supposed in stating that the workers have no country, it probably advanced among the working class pari passu with political consciousness, if only because the tradition of revolution itself was national (as in France) and because the leaders and ideologists of the new labour movements were themselves deeply involved in the national question (as almost everywhere in 1848). The alternative to a national political consciousness was not, in practice, working-class internationalism but a sub-political consciousness which still operated on a scale much smaller than, or irrelevant to, that of the nation-state. The men and women on the political left who chose clearly between national and supra-national loyalties, such as the cause of the international proletariat, were few. The internationalism of the left in practice meant solidarity and support for those who fought the same cause in other nations and, in the case of political refugees, the readiness to participate in the struggle wherever they found themselves. But, as the examples of Garibaldi, Cluseret of the Paris Commune (who helped the Fenians in America) and numerous Polish fighters prove, this was not incompatible with passionately nationalist beliefs.
It might also mean a refusal to accept the definitions of the national interest put forward by governments and others. Yet the German and French socialists who in 1870 joined in protesting against the fratricidal Franco-Prussian war were not insensible to nationalism as they saw it. The Paris Commune derived its support from the Jacobin patriotism of Paris as much as from the slogans of social emancipation, and the Marxist German Social Democrats of
Liebknecht and Bebel derived much of theirs from their appeal to the radical-democratic nationalism of 1848 against the Prussian version of the national programme. What German workers resented was reaction rather than German patriotism; and one of the most unacceptable aspects of reaction was that it called Social Democrats vaterlandslose Gesellen (fellows without a fatherland), thus denying them the right to be not only workers but good Germans. And, of course, it was almost impossible for political consciousness not to be in some way or another nationally defined. The proletariat, like the bourgeoisie, existed only conceptually as an international fact. In reality it existed as an aggregate of groups defined by their national state of ethnic/linguistic difference: British, French or, in multinational states, German, Hungarian or Slav. And, in so far as state and nation were supposed to coincide in the ideology of those who established institutions and dominated civil society, politics in terms of the state implied politics in terms of the nation. (pp.114-17.)
[Developments in education; proportion of increase in US, and Britain, France and Germany (gymnasia) 
[European Jews; Yiddish/Mame-Loschen]
The paradox of nationalism was that in forming its own nation it automatically created the counter-nationalism of those whom it forced into the choice between assimilation and inferiority. / The age of liberalism did not grasp this paradox. Indeed, it did not understand that principle of nationality which it approved, considered itself to embody, and in suitable cases actively supported. (p.12).
Nationalist therefore seemed readily manageable within the framework of bourgeois liberalism, and compatible with it. A world of nations, would, it believed, be a liberal world, and a liberal world would consist of nationals. The future was to show that the relationship between the two was not as simple as this.