Final answer:
The Prevailing Westerlies are the major wind belt that affects the eastward movement of weather systems in the USA, which together with the Jet Stream, significantly shapes the country's climate patterns.
Step-by-step explanation:
The major wind belt that contributes to the eastward trek of weather systems in the USA is the Prevailing Westerlies. These winds generally blow from the west to the east in the mid-latitudes between 30 and 60 degrees latitude. They are one of the three major wind belts that also include the Trade Winds and the Polar Easterlies. The Jet Stream, while not a wind belt, is a narrow band of strong upper-level winds in the atmosphere that can have a significant influence on the movement of weather systems and is also a key factor in the movement of weather systems across the USA.
Wind systems are crucial in determining weather patterns. For example, the Prevailing Westerlies not only move weather systems but also interact with other factors like ocean currents, elevation, and mountain barriers to shape temperature and precipitation patterns, therefore influencing the distribution of climate regions as outlined in WG.4A.