Conversation so far:
who won the war between spain and france
At Vitoria, Spain, a massive allied British, Portuguese, and Spanish force under British General Arthur Wellesley routs the French, effectively ending the Peninsular War.
why was the peninsular war important
The Peninsular War is regarded as one of the first wars of national liberation, significant for the emergence of large-scale guerrilla warfare.
how long did the peninsular war last
The Peninsular War lasted 5 years, 11 months, 2 weeks and 1 day.

Question: What caused the war?
Self-contained rewrite: What caused the Peninsular War?