These and other issues greatly worried many of the Founders that the Union as it existed up to that point was in danger of breaking apart. In September 1786, delegates from five states met at the Annapolis Convention and invited all states to a larger convention to be held in Philadelphia in 1787. The Confederation Congress later endorsed this convention "for the sole and express purpose of revising the Articles of Confederation". Rhode Island was the only state that refused to send delegates, though it would become the last state to ratify the Constitution, in May 1790.