1)Yes, sometimes war is the solution of different problems which exist between different countries or religion because war is the only resort when countries fail to solve an issue through diplomatic or economic arrangements. Although war causes massive bloodshed and destruction, sometimes it is the only way to bring peace.
2) Countries or nations fight wars for a number of reasons. First of all, two or more countries may begin a war for the sake of "expansion" of the territory. Secondly, wars are fought by the nations to get back their countries from foreign rulers or invaders.
