1. French Naval Support: The French fleet commanded by Admiral de Grasse arrived in Chesapeake Bay on September 5, 1781, blocking the British fleet under Admiral Thomas Graves from providing reinforcements or supplies to Cornwallis's forces at Yorktown.
2. American and French siege: American and French forces led by General George Washington and General Jean-Baptiste Donatien de Vimeur, comte de Rochambeau mounted artillery batteries around the British fortifications, subjecting the British to heavy bombardment and making it difficult for them to move or maneuver.
3. Failed British attack: British General Charles Cornwallis attempted a surprise night attack on the American and French positions on October 16, but the attack was poorly planned and executed and was easily repelled.
4. Poor British Leadership: Cornwallis' decision to remain at Yorktown, despite the French fleet's arrival, and his failure to take decisive action to break out of the siege.
5. Lack of reinforcements: The British government failed to provide Cornwallis with the necessary reinforcements and supplies due to their commitment to the war in the Caribbean and Europe.
The combination of these factors forced Cornwallis to surrender his army to the combined American and French forces on October 19, 1781, marking the end of the major military conflict in the Revolutionary War.