Hungary, officially the Kingdom of Hungary (Hungarian: Magyar Királyság) was a sovereign state in Central Europe, established in 1920 after the fall of the Hungarian Soviet Republic. It was a de facto regency state under Regent Miklós Horthy officially representing the abdicated Hungarian monarchy. Attempts by Charles IV King of Hungary to return to the throne were prevented by threats of war from neighbouring countries, and by lack of support from Horthy. Hungary participated in the invasion of Czechoslovakia in October 1938 on the side of Nazi Germany, and following the conquest of Czechoslovakia in March 1939, Hungary annexed the territories of Slovakia and Carpatho Ruthenia.