Complex sentence: Czechs soon found the need to culturally organise themselfes and in 1874 first "Česka Beseda" (Czech word) was found in Zagreb, organization that promotes Czech language and culture in Croatia and organised first theater play in Czech language same year.
Split into simpler sentences: Czechs soon found the need to culturally organise themselfes and in 1874 first "Česka Beseda" (Czech word) was found in Zagreb. This is an organization that promotes Czech language and culture in Croatia, and organised the first theater play in Czech language in the same year.