Russians invade other countries because they are not capable to produce good things by themselves. They need someone to build advanced weapons, armor, ships, planes, rockets, goods for export. Good warriors are bad makers, usually.

For example, if you are incapable to build a house, then you need to hire someone to build it for you. If you have no money, but you have an army, then you can just enslave him instead. Russian Empire is the jail of nations.