During the last century, the number of states around the world grew dramatically. In 1900, the world was divided into about 50 states. The “imperial” interstate system was a heterogeneous collection of multinational empires and their colonies, monarchies, dictatorships, and republics, most of the latter located in the Americas. By 2000, the interstate system consisted of more than 190 states, most of them nation-state republics, making it a more homogeneous system than its predecessor.
The number of states increased dramatically as a result of several important developments: decolonization, partition, secession, and devolution. These “separatist” political processes contributed first to the breakup of multinational imperial states and then of nation-state republics, and the creation of numerous successor states in their place. In coming years, the number of states in the interstate system will likely increase as a result of partition and secession.
The breakup of empires helped solve problems associated with the inter-imperial rivalries that led to two world wars in the first half of the century. And the proliferation of states associated with decolonization, partition, and secession has given people around the world the opportunity to practice self-government in states of their own. But these separatist political processes have also been difficult and contentious and sometimes led to conflict and war within and between states.