Allied invasions that denied bases to the Axis

Which neutral states or colonies did the Allies invade to keep them out of Axis hands, and was that strategy justified?

The discussion names Iceland and Madagascar among several cases; Madagascar had a clear denial rationale because Japanese access could threaten Allied sea routes, while other occupations require more case-by-case judgment.

Iceland and, more tentatively, Greenland are named among places occupied to deny access to the Axis. The answer also points to Madagascar and a wider set of French colonial possessions around Africa and Southeast Asia. Madagascar receives the clearest strategic explanation: Britain feared Japanese seizure would introduce a new base and ocean route into the wider Battle of the Atlantic problem. That operation made sense in its wartime context, though the same judgment may not apply to every preventive occupation. The exchange concerns denial of geography and logistics without presenting such invasions as politically uncomplicated.