Mariann was born in the town of Nagykőrös in Hungary, then part of the Austro-Hungarian Empire. The Empire was formed in 1867 under Austrian Emperor Franz Joseph, combining the power of Hapsburg-led Austria with that of Hungary. The Empire also included Croatia, Bosnia and Herzegovina, Slovenia, Slovakia, as well as part of what are now Serbia, Romania, Ukraine, Poland, and the Czech Republic. Read more about Franz-Joseph and the formation of the dual monarchy here.
After the First World War and the collapse of the Empire in 1918, Hungary briefly became an autonomous, socialist nation, first under Mihály Károlyi, and later Belá Kun. Under Kun's administration, Hungary briefly went to war with Romania; this period is known as the Red Terror. In response to this, a series of violent anti-communist attacks and riots took place; this period is referred to as the White Terror. Read more about Hungary in the interwar period here.
For an overview of Hungary's involvement in the First World War, the subsequent peace negotiations, and political turbulence, read this article.
In 1920, Admiral Miklos Horthy took control, taking up the position of "regent".
Following the massive economic downturn of the 1929 Great Depression, Hungary's enconomy gradually improved, largely through trade with Germany. Hungarian authorities fostered a positive relationship with Germany, feeling that the policies of its National Socialist government was in line with Hungary's own aims and values.
A result of this relationship was that in the 1938 Munich Agreement, negotiated between the major Western powers and Germany, Hungary received back some of the territories it had lost in the Treaty of Trianon after World War One. The 1938 Agreement was signed between England, France, Italy, and Germany. This Agreement ceded the Sudetenland to Germany, dividing Czechoslovakia. British Prime Minister Neville Chamberlain, a key figure in the negotiations, believed appeasing Adolf Hitler’s territorial ambitions was the most logical way to avoid another large-scale war. Read more about Chamberlain’s policy of appeasement here. The agreement was negotiated among Europe’s major powers without any Czechoslovakian representative- today’s Czechs and Slovakians often refer to the agreement as "the Munich dictate" or the "Munich betrayal". Read a transcript of the original text here.