Is the Treaty of Trianon Fair?

The answer to this question is very simple: no. I'd just like to list a couple of facts to prove that statement:

1.The Kingdom of Hungary was not a sovereign state at the outbreak of the war. While it is true that she enjoyed quite a significant autonomy within Austria-Hungary,the external affairs were always decided by the kaiser,Franz Joseph,therefore Hungary did not have a say nor a choice but to participate in the war.

2. After the borders were carved,millions of Hungarians found themselves outside them,out of which again millions lived right next to the new borders,still there are grave conflicts because of this between for example Slovakia and Hungary and the local populations too; it is prohibited to speak Hungarian in Slovakia even up to this date and there are still more than half a million ethnic Hungarians in that country.

3. The main principle of the Antante powers (at least that is what they said) when drawing the new borders was to provide sovereignty to the different nations in the area,saying that such a multiethnic country as Hungary was can not exist anymore. This,of course,was hipocratic,lets just look at the ethnic composition of the Kingdom of Serbs,Croats and Slovenes: there were obviously Serbians,Croatians,Slovenians,Hungarians,Bosnians,Montenegrins,Albanians,Macedonians,Germans and some other nationalities in smaller numbers like

Romanians and Bulgarians. The same can be said about Czechoslovakia( Germans,Czechs,Slovaks,Hungarians,Ruthenians) and Romania(Romanians,Hungarians,Ukranians,Bulgarians)

There are countless other reasons why the answer to your question is no,but i think i gave a brief outline of some important points.