Final answer:
Napoleon sold the Louisiana Territory due to the high costs of his European wars, the prospect of conflict with Britain, and the financial and military strains after the failed campaign in Haiti and the disastrous Russian invasion.
Step-by-step explanation:
Napoleon Bonaparte reconsidered his ambitions for a North American empire primarily due to financial strains and military setbacks. The expense of the failed war to maintain control over the colony of Haiti, along with the looming prospect of a new war with Britain, strained French resources. Additionally, the loss of the ability to directly threaten Britain after the naval defeat at the Battle of Trafalgar forced Napoleon to focus on continental Europe. Consequently, Napoleon sold the Louisiana Territory to the United States for fifty million francs, which in today's money would be about $11 million. This decision also made strategic sense, as it ensured the valuable territory wouldn't easily fall into the hands of the British should war break out, and it provided funds to rebuild the French army, especially after the disastrous Russian campaign that damaged Napoleon's reputation as a military leader.
Furthermore, Napoleon's continuous need for victory and expansion led to a costly invasion of Russia in 1812, which ended disastrously and weakened his forces significantly. He had built a vast empire through conquests, but the Russian campaign proved to be a turning point, showing his vulnerabilities and propelling his downfall. The losses in Russia, alongside the need to maintain and rebuild his army, made the upkeep of a distant North American empire impractical. This sale, known as the Louisiana Purchase, significantly expanded the territory of the United States.