The Louisiana Purchase is one of the greatest achievements of any American government ever. In the first place, the US acquired a huge territory of 828,000 square miles, the largest land bargain in American history. It was a vast, rich and unexplored area. Secondly, it brougt the US closer to the western part of the continent, closer to the Pacific Ocean. Thirdly, many states that later joined the Union evolved from the original purchased area of Louisiana. And fourthly, the US doubled its size, with its material and strategic advantages, and westward expansion got a phenomenal boost.
The war started mainly because of four aspects Militarism Alliances Imperialism and Nationalism. This is because big armies become potential threats to other countries.