Complex sentence: On August 20 and 21,1781, Congress expressed conditions that must be met before the then still unrecognized but de-facto independent state could be admitted into the Union, including extinguishment of Vermont's claims to any territory east of the river.
Split into simpler sentences: On August 20 and 21,1781, Congress expressed conditions that must be met before the then still unrecognized but de-facto independent state could be admitted into the Union. Among the conditions was extinguishment of Vermont's claims to any territory east of the river.