In the wake of the Munich agreement of September 1938, Germany and Italy supported Hungarian claims to the southern part of Slovakia. Bi-lateral negotiations broke down between Czechoslovakia and Hungary in October, but on November 2, 1939 German diplomatic intervention resulted in the First Vienna Award. Slovakia had to cede territory that in 1910, had a majority Hungarian population. The Czech's resisted and used their 1930 census to show this territory was no longer majority Maygar. German pressure was to great and this territory was ceded more or less peacefully. One bridge was blown up and one Slovakian railroad manager was killed, but no large scale battle was fought.
Hungary also had claims on Transylvania. With German and Italian diplomatic support, Hungary was able to annex a slice of Transylvania from Romania. In this case, the Hungarians did not get all of what they wanted, because Germany did not want to punish Romania too much. This transfer was formalized at the Second Vienna Award, on August 30, 1940.
Source: Dinu Grurescu "Romania in the Second World War"
I can only give you a short answer: no, there was no serious international movements fighting to revise the borders based on ethnic principles. The Munich and Vienna agreement at the wake of the Second World War was certainly not backed by any international movement or a lobbying force, it was merely a political decision made by the biggest power(s) of Europe with a strategic interest in that region.
However, attempts were made by Hungary to 'spread the word' in the interwar period. There was a British journalist, one of the founders of Daily Mail and Daily Mirror, Lord Rothermere (Harold Harmsworth) who supported a revision of post-WW1 treaties. In his famous article (well, only became famous in Hungary), Hungary's Place in the Sun published in 1927 in Daily Mail, he argued that the postwar settlements have created many tiny Alsaces in this region (refering to Alsace and Lorraine as their belonging have sparked many wars between Germany and France). Thus it is Biritsh interest to settle down the ethnic disputes in the region to prevent another war and secure a peaceful future and cooperation for the successor states of Austria-Hungary. Lord Rothermeres article made the headlines in Hungary, he become very famous and even nowadays his actions are an important part of the national historical narrative. But his efforts made no impact whatsoever in international politics.
Also, there was government-backed organization, the Hungarian Revisionist League (Magyar Revíziós Liga) whose declared aim was to spread the word about the unjustful postwar settlement. It published hundreds of articles, books and pamphlets in England, France and Italy. Once again, it's impact was trivial.