Why were France and England rivals?

Too Close For Comfort

Beginning in the Middle Ages, England and France were in proximity, each having the nearest undeveloped lands to the other. Although both eventually engaged in wars with other nations in Europe and the world, it was logistically simpler to mount an armed conquest on a neighboring country. As colonies developed, the countries gained more resources abroad, but each sought advantages. As the Napoleonic Wars showed, a country with sufficiently developed armed forces could conquer and annex large regions of Europe. It was not until the 20th Century wars that England and France became reluctant allies, both having also lost almost all of their colonial empires.