Khar'shan, the batarian homeworld, is wrapped less in mystery than in outright lies. Batarian propaganda claims the world has 15 billion inhabitants and an economy that rivals the asari. Although the legal slave trade does boost the batarians' profits somewhat, Citadel sanctions have left a paper tiger of an empire, one that fights rivals through deniable terrorist actions rather than the wars of its heyday centuries ago.
Mass Effect 3
The Reapers first invaded Batarian space. After destroying the comm buoys the Reapers set their sight on Kar'shan, laying it to waste. In conversation with Shepard, Balak claims that the Reapers were aided by a number of indoctrinated Batarian scientists who were working on the Leviathan of Dis. These scientists managed to disable a number of key defense grids on the planet rendering resistance to the Reapers futile and causing a number of Batarian ships in the fleet to fire on one another. Balak claims he is the highest ranking military officer left in the Hegemony which gives an indication of how thoroughly destroyed the Batarian military was.
Almost no information has escaped Khar'shan since the Reapers destroyed the comm buoys, but batarian refugees say that resistance has created a bond among commoners. If a new government can rise from the ashes, that bond may sustain a new batarian society.