Over a period of 15 years, from 1774 to 1789, the Continental Congress underwent a profound evolution. Starting out as a temporary group that met to address American colonists’ issues with British rule, it morphed into the de facto government of the 13 colonies, and ultimately into an official governing body of the United States.

These different phases of the congress  are often referred to as the First Continental Congress, Second Continental Congress and Confederate Congress. Here are the major achievements of each.

The First Continental Congress began under British rule in September 1774. Comprised of 56 delegates from 12 of the original 13 colonies, the group met in Philadelphia and lasted less than two months. It focused mainly on how to respond to the British Parliament’s passage of the Intolerable Acts—also known as the Coercive Acts—a series of repressive acts designed to restore order to Boston after the Tea Party and punish the colonists for their bold insurrection. During its short meeting time, the Continental Congress compiled a list of grievances that it sent to Britain’s then-ruler, King George III. It also adopted the Articles of Association, which initiated a boycott of British goods by the colonies.

The Articles of Association stand as the First Continental Congress’s most important accomplishment, says Benjamin H. Irvin, a history professor at Indiana University Bloomington and author of Clothed in Robes of Sovereignty: The Continental Congress and the People Out of Doors. In addition to the boycott, the document authorized the creation of local committees to help with the transfer of power between Britain and the colonies.

Unlike later versions of the Continental Congress, the first one didn’t see itself as a governing body. The British Empire was still the recognized governing authority, and the Articles of Association that the First Continental Congress issued was not a law. Even so, “the Continental Congress did take measures to prepare the colonists for the possible overthrow of British authority,” Irvin says.

“The Congress endorsed the Suffolk Resolves, in which the people of Suffolk County, Massachusetts, determined ‘to acquaint themselves with the art of war,’” he says. And by calling on local communities to establish committees of inspection in the Articles of Association, “Congress readied the American people to throw off British rule and establish local government.”

The Second Continental Congress started in May 1775, less than a month after the first Revolutionary War battles at Lexington and Concord. This time, the Continental Congress’s role was different, as it became the de facto government of the 13 colonies during their war with the British Empire.

“The delegates wasted no time deliberating the nature or extent of their authority; instead, they convened in the spirit of a council of war,” says Irvin. The Continental Congress established an army, a navy and a post office, and issued currency. “In this manner, and without hesitation, the Continental Congress began to assume legislative and executive responsibility.”