Unlike the Treaty of Versailles with Germany Trianon is not, I suspect, given much attention today in western Europe or the US, which is unfortunate. In Hungary itself it remains a matter of continuing bitterness. Just as the Treaty of Versailles can be seen as paving the way for trouble within a generation so Trianon created as many tensions, indeed probably more, which produced in the mid-century the very thing the authors had sought to avoid.
To understand the Treaty and its background I would strongly recommend reading the article on Wikipedia. This appears balanced and looks at, for example, the debates on both sides about defining nationality on the basis of the 1910 census. It can be seen at Treaty of Trianon
To accompany the maps in that there is a huge selection available, some statistical and some more in the way of propaganda, which can be found at Hungary lost territory
Having looked at that and with some historical knowledge here are my thoughts. I have, by the way, no ancestral link to any of the nations affected by the changes brought about by the Trianon treaty.
Firstly this was the deliberate destruction of a kingdom that had more than a millennium of history, and all that means in shared experiencess, behind it, and which had been a bulwark against Mongol and Ottoman invasion - both of which had wrought terrible harm.
That there had been in the years preceding 1914 a government in Budapest which had stressed Magyar identity at the expense of others within the realm is true. At that same time in Britain, France, Italy, Prussia and Russia - never mind Turkey - cognate policies were pursued. In all of them national identity was stressed at the expense of local communal and linguistic ones. So British liberals who wrote about the minority problem in Hungary might have gained from visits to Wales, Ireland or Gaelic Scotland.
The ancient Hungarian realm was dismantled in favour of national self determination - yet as the Wikipedia article shows in reality the new successor states were left with sizeable minorities who were very concerned to assert their Magyar identity, and who were faced with attempts to make them Yugoslav, Czechoslovak or Romanian. We only have to look at the history and map of modern Europe to see what a success the first two of those states were.
A sizeable part of the Magyar population and their homelands were assigned to countries to which they felt no alleigance, separated from their fellow Magyars in the rump of historic Hungary. Territories were largely transferred as county units, not as quantified national groupings.
Only one plebiscite was held, and that for a small area. National self determination was at the stroke of a foreign diplomat’s pen rather than at the ballot box. The talk of the rights of small nations was shown to be that - talk.
Thus to resolve the problem of a Romanian minority in Hungary - where there had been traditions of local Transylvanian autonomy - the answer in 1920 was to create a Hungarian minority in Romania. A century later that remains a fact of Transylvanian life.
To elevate national self determination to the highest point was dangerous in so many ways. What at the same time for the Irish ( or some of them), the Scots, the Bretons or the Corsicans, let alone colonial empires. The shrill voice of national self determination and nationalism can easily become the popularist cry for integrating into the Fathetland all the volk irrespective of historic boundaries...
To apply such a policy and still to leave swathes of debatable lands with mixed populations suggests disdain for the defeated and a bland indifference to others and their identities.
Faced with such a fait accompli there is little wonder that interwar Hungary was geared to redraw its borders. This it achieved in 1938 and 1940, but we know the fate of him who sups with the devil. Even with a return to the 1920 frontiers Hungarian resentment survived, and since 1989 that sense of loss can be freely articulated in word and artwork.
How peoples reconcile differences consequent on language, ethnicity and religion is not easy, but if they have managed to coexist for centuries reasonably well, then is it not best put in place measures to reinforce that, and not to tear up the map. If Switzerland can manage four languages and two religious confessions, or Belgium, with periodic testing up of the cobblestones as missiles, with three languages, why cannot other countries do so to their mutual economic and social advantage? The shrill cries of nationalism, encouraged for cynical reasons by outsiders, should not have been allowed to prevail.
The Treaty of Trianon and its baleful legacies are just further proof of what an unmitigated disaster the slide into war, and war to achieve an absolute victory at that, was in 1914. It is also further proof of the blinkered, selfish and cynical attitudes of too many of those seeking to establish peace in its aftermath.