In Hungary, like in Germany, public opinion was unhappy with the treaty which ended World War I and left territories inhabited by large numbers of Hungarians outside the country's borders. Horthy's Hungary had expansionist aims, and Nazi Germany was willing to make border adjustments in the country's favor - Czechoslovakia and Yugoslavia, which Nazi Germany dismembered, and Romania, which, while ultimately allying with Nazi Germany, was neutral at the time, had large Hungarian populations which Horthy's regime was able to reunify with Hungary.

Furthermore, there were ideological reasons for an alliance. Hungary was ruled by a short-lived communist regime in the immediate aftermath of World War I, and Horthy's regime came to power by overthrowing it. He was strongly anti-communist and had obvious reasons to support the idea of toppling the Soviet Union.

It should also be noted that Hungary and Germany were not equal partners. The reason Hungary was able to seize territory from Yugoslavia and Romania was that the regimes there were reluctant to support Nazi aims and were punished with invasion after an anti-Axis coup in the former case, and territorial seizures in the latter. Hungary had a homegrown fascist movement of it's own, whose leaders Hitler would ultimately install after Horthy attempted to surrender to the Allies, and Horthy, while certainly a more enthusiastic ally than others, had a practical reason to go along with German policy to stay in power.

I don't personally know of any resistance movements (save the Hungarian Communist Party, although its ability to undertake actual resistance in the interwar period was minimal) but that shouldn't be taken to mean none existed; I'm more familiar with Hungary as it relates to the World Wars than its domestic politics.