Capitalize compass directions only when they refer to specific geographic regions, such as the South. On his journey north Gawain encountered few obstacles. (He is heading in a northward direction but not traveling to a region known as the North.) ... (Some grammarians capitalize long prepositions.)

Should Southwest be capitalized?

When using north, south, east, and/or west (and variations) lowercase them when referring to directions and capitalize them when referring to regions. In the first sentence, southwest is a direction, so it remains lowercased. In the second sentence, Southwest is a region, so it gets capitalized.

Should Commonwealth be capitalized?

3.20. The similar designations commonwealth, confederation (federal), government, nation (national), powers, republic, etc., are capitalized only if used as part of proper names, as proper names, or as proper adjectives.