Originally Posted by the new

The Army's counterinsurgency handbook contains an admonitory example of what happens when campaigns are not well designed.

When Napoleon occupied Spain in 1808, he and his commanders gave little thought to how difficult it might be to subdue the Spanish population. Though the French had won an easy initial military victory, they quickly became enmeshed in a protracted struggle with insurgents that lasted six years. In the end, Napoleon had to deploy four times as many troops as he had started with.

The effort drained the resources of the French empire. "It was the beginning of the end for Napoleon," according to the US Army manual.