Final answer:
The Capture of Fort Ticonderoga by Ethan Allen and the Green Mountain Boys is the important event that happened at Ticonderoga in winter 1775. This event provided the American forces with valuable artillery and military supplies.
Step-by-step explanation:
The important event that happened at Ticonderoga in winter 1775 was the Capture of Fort Ticonderoga by Ethan Allen and the Green Mountain Boys. This event is significant because it provided the American forces with valuable artillery and military supplies. It also boosted American morale and demonstrated their ability to challenge British authority.