Recentish example. Russia invade Georgia. USA impose trade restrictions (hitting them in the wallet....). Russia respond by banning imports of American chicken, a $1 Billion industry. 500,000 chicken industry workers are voters. Obama lifts the restrictions rather than lose the votes. And that's only $1 billion, imagine how much control the oil industry has.
It's always about money Saul and the politicians are at the mercy of the people who have it. Child slavery, and a whole bunch of other stupid and ugly human behaviours happen because of money (and the greed for it and the power it brings) and where do those multinationals get their money from so that they can lobby and pressure politicians to keep those civil wars going?