It's difficult to say which two communities are the *most* important, as different communities hold different significance in the Northwest Territories. However, two communities that stand out for their historical and cultural importance are:

1. Yellowknife: The capital city of the Northwest Territories, Yellowknife is the largest community with a vibrant economy, diverse population, and significant history in the diamond mining industry.

2. Fort Smith: Historically known as "the gateway to the North," Fort Smith is located at the junction of the Slave River and the Mackenzie River. It's a significant hub for transportation and resource extraction, as well as a centre for Dene and Métis culture.

Choosing just two is subjective, and many other communities like Inuvik, Hay River, and Fort Resolution are important in their own right. Each community contributes uniquely to the social, economic, and cultural landscape of the Northwest Territories.