That is not entirely true. Governments, unlike individuals, are fairly rational agents and do not start wars for revenge. For all we care, the murdered president was member of the opposition and his disposal might have helped the current ruling party.
I think you are being overly generalist here. Governments are as rational as the people that make them and run them, in the same way as a corporation (or any group of people, really). Can you really say that all governments are fairly rational? How about North Korea?
At least the motive of corporations is clear: profit. A (democratically elected) government is in constant conflict with itself over ideology (a much trickier motive to grasp, one that often causes irrational behavior), and it doesn't always take consensus to act.
