Battle or Siege of Yorktown took place today.

AMERICANS
Continental Infantry 7,290
Artillery 514
Cavalry 176
Total Continental Army 7,980
Militia 3,153
Total (non adjusted for effectives) 11,133
Non-effectives (sick)
absent
present
-1,000
-700
Total Effectives ('rounded figure') 9,500
FRENCH
Rochambeau's 4,000
St. Simon's 3,000
Army detachments [See note at bottom of page] 800
Naval personnel
abord ships, in
direct support. 1,000
Total 8,800
Excluding est 15,000 naval personnel
on ships that contributed to the overall
campaign.
TOTAL ALLIED FORCE 18,300
BRITISH
'Reported' army strength at start.
Includes German mercenaries. 8,885
Estimated naval personnel
directly supporting 840
Estimate naval personnel figure is
from number that surrendered to de Grasse.
Estimated British total at start 9,725
Estimated sick -1,500
TOTAL BRITISH FORCE 8,225

(The preceding is based upon data from Mark Mayo Boatner III Encyclopedia of the American Revolution (p.1248, Bicentenial Edition, NY, 1974).

It was THE victory of the American Revolutionary War. A combined French/Continental(American) army surrounded, besieged, and forced the surrender of a larger by most estimates British Army under Lord Cornwallis. The defeat sealed the fate of the British dominion over what would become the United States of America and lead directly to the Treaty of Paris.

One of the results of the French intervention was the bankrupting of the French Royal Treasury which was one of the reasons for the Revolution in France. Although Britain did lose this particular theater, she went on to completely trounce the French and Dutch in such far off places as India and the Carribean. The Revolutionary War as we call it was but a part of what could be called one of the first global wars ever fought.
Links:

http://www.u-s-history.com/pages/h1321.html
http://xenophongroup.com/mcjoynt/yrtnsieg.htm
http://encarta.msn.com/encyclopedia_761562639/siege_of_yorktown.html
http://en.wikipedia.org/wiki/Siege_of_Yorktown