Which event most directly led to cornwallis’s being trapped at yorktown and compelled to surrender?

a. the entry of france & spain into the war
b. washington's surprise crossing of the delaware
c. britain's failure to take control of the southern states
d. the outbreak of conflict with the native americans on the frontier

C. Britain's failure to take control of the southern states

Explanation:

Cornwallis decided to conquer Virginia, to which the loyalist army of traitor Arnold was moving. The union of the two armies happened on May 20th. It should be noted that during 1781 Cornwallis suffered several defeats on its way to Chesapeake Bay. The most famous are the defeats at King's Mountain and at Cowpens.

Washington and Rochambeau realized that the British army was in a very awkward position on the peninsula between the York and James rivers

and they decided to take advantage of it. It also came to their knowledge that a large fleet led by Admiral de Grasae had left France on May 21, 1781, and would finally arrive in Virginian waters on August 11. The British were unaware of such circumstances and were sending a fleet led by Hood and Graves to Chesapeake Bay. General Clinton, who held a strong British army in New York, did not have the courage to send her to Chesapeake Bay because he was not sure who the Americans and their allies intended to attack. On September 5, the British Navy came to the bay, but was met with an unpleasant surprise. They realize they are outnumbered and after a few exchanges of cannon fire, decide to return to New York security.

Fort York, where Cornwallis hid, was surrounded on all sides by 5,700 US troops, 7,000 French, and 3,000 militiamen.113 After a two-month siege, Cornwallis had only left to surrender his 7,000 troops. The surrender occurred on October 19, 1781.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.