State law concerning use of force

The law concerning use of force is a contentious area in international law. In pre-modern times, the state territory was extended by occupying a certain area forcefully; the rights over that property of the occupied land vested with the state annexing the land. It was simple and easy to occupy a certain territory since there were no laws between the states. Now, with the UN Charter, the rights have been laid down and every state is under an obligation to respect the boundaries of other  states  and  use  of  force  against  other  state  is  prohibited. The  most  fundamental  and significant contribution of law between states is exercised by the UN Charter 1945.