The Confederation period was the era of United States history in the 1780s after the American Revolution and prior to the ratification of the United States Constitution. In 1781, the United States ratified the Articles of Confederation and Perpetual Union and prevailed in the Battle of Yorktown, the last major land battle between British and American Continental forces in the American Revolutionary War. American independence was confirmed with the 1783 signing of the Treaty of Paris. The fledgling United States faced several challenges, many of which stemmed from the lack of a strong national government and unified political culture. The period ended in 1789 following the ratification of the United States Constitution, which established a new, more powerful, national government. The Articles of Confederation established a loose confederation of states with a weak confederal government. An assembly of delegates acted on behalf of the states they represented. This unicameral body, officially referred to as the United States in Congress Assembled, had little authority, and could not accomplish anything independent of the states. It had no chief executive, and no court system. Congress lacked the power to levy taxes, regulate foreign or interstate commerce, or effectively negotiate with foreign powers. The weakness of Congress proved self-reinforcing, as the leading political figures of the day served in state governments or foreign posts. The failure of the national government to handle the challenges facing the United States led to calls for reform and frequent talk of secession. The Treaty of Paris left the United States with a vast territory spanning from the Atlantic Ocean to the Mississippi River. Settlement of the trans-Appalachian territories proved difficult, in part due to the resistance of Native Americans and the neighboring foreign powers of Great Britain and Spain. The British refused to evacuate US territory, while the Spanish used their control of the Mississippi River to stymie Western settlement.