Conflict or war is always beneficial to the countries or government that sent themselves out to surpress the other lesser countries.
Economic Gain
Often wars are caused by one country's wish to take control of another country's wealth. Whatever the other reasons for a war may be, there is very often an economic motive underlying most conflicts.
Territorial Gain
A country might decide that it needs more land, either for living space, agricultural use, or other purposes. Territory can also be used as “buffer zones” between two hostile enemies.
Religion
Religious conflicts often have very deep roots. They can lie dormant for decades, only to re-emerge in a flash at a later date.

Religious wars can often be tied to other reasons for conflict, such as nationalism or revenge for a perceived historical slight in the past.