Wars are fought with money, and in the War of the Five Kings, none of the Great Houses are more financially equipped than the Lannisters. They outfit their troops in the best armor and arm them with the finest steel. But troops still need leaders.
-Some show their strength on the battlefield, like the Hound, Tyrion, or Lord Tywin. For others, like Maester Pycelle and the High Sparrow, their power is felt in the political arena. But make no mistake, they can influence the outcome of a battle all the same.