Three periods of time are going to be analysed to a large extent:

1. First, the period following the Russian Revolution and the end of the World War I, that drastically changed Europe and the world. Four empires collapsed and new states were formed. In 1918, Poland regained its independency after the collapse of the Czarist, German and Austrian Empires. Rumania achieved its greatest territorial extent after these powers were defeated. 
2. Second, the post-World War II consolidation of former subordinate states. The 1918 collapse of the Ottoman Empire did not result in the direct creation of independent states in the Arab world but in its division between France and the British Empire. Egypt was nominally a part of the Ottoman Empire but after the declaration of war against it, Britain seized the opportunity to declare a Protectorate over Egypt. Egypt was occupied by the British since 1882, but was officially protectorate since 1914, and until 1956 the British troops did not withdraw. And Morocco was a French protectorate since March 1912 and was not independent until 1954, with a gradual annexation of former Spanish protectorate and colonies in the region (Tánger, Ifni, Rio de Oro province…). 
3. Third, the period following the breakdown of the Union of Soviet Socialist Republics, i.e., the period after 1989/1991. This period is hit by less violence but intrinsically it was not very different. When the Soviet empire was disassembled, new/old states became independent. States that enjoyed limited sovereignty before gained full independence and they were able to go their own ways in the field of international politics. The splitting of former states gave birth to new ones: Ukraine, Byelorussia, Turkmenistan, Azerbaijan, Kazakhstan and other states emerged from the lands of the former Soviet Union; the Czech and the Slovak republics were created after the breakdown of Czechoslovakia.