Short answers, pulled from the story.
Stephen I became the first king of Hungary on Christmas Day 1000 when he accepted baptism and took his royal name at the cathedral in Esztergom. This event marked the transition from a pagan Grand Principality to a Christian Kingdom under the Árpád dynasty.
Mongol armies under Subutai destroyed the combined Hungarian and Cuman forces at the Battle of Mohi in 1241, causing an estimated five hundred thousand to one million deaths. Béla IV rebuilt the kingdom after the invasion by erecting numerous fortresses across the land and earned the title Second Founder of the Homeland for these efforts.
The central authority collapsed immediately after King Louis II drowned in the Csele Creek on the 29th of August 1526, leaving the country divided into three parts. Royal Hungary remained under Ferdinand I in the north and west while Ottoman Hungary controlled the Great Alföld region including south-eastern Transdanubia.
The Austro-Hungarian Compromise transformed the monarchy into a dual state with equal status for Austria and Hungary in 1867 when Francis Joseph I and Elisabeth were crowned at Matthias Church in Buda on the 8th of June 1867. GNP per capita grew roughly 1.45 percent per year from 1870 to 1913 under this arrangement.
The Treaty of Trianon signed in 1920 ceded seventy-two percent of the territory of the Kingdom of Hungary to neighboring states. More than three million ethnic Hungarians found themselves separated from their motherland by these new borders.
In 1946 the form of government was changed to a republic ending the monarchy that had existed since 1000. The Soviet Union pressed Mátyás Rákosi to take a line of more pronounced class struggle leading to a communist state lasting until 1956.