How did some European countries like Lithuania, Hungary and Denmark go from large medi empires to such small and weak states?

立陶宛、匈牙利和丹麥等歐洲國(guó)家是如何從中世紀(jì)的大帝國(guó)變成現(xiàn)在這樣如此小的弱國(guó)的?