Complex sentence: In 1803 he invited the leaders on the local tribes to Vincennes where they signed a treaty recognizing American possession of the Vincennes tract, that had been captured by George Rogers Clark in the American Revolutionary War from the French.
Split into simpler sentences: In 1803 he invited the leaders on the local tribes to Vincennes where they signed a treaty recognizing American possession of the Vincennes tract. This area had been captured by George Rogers Clark in the American Revolutionary War from the French.