Communist here means >50% of the population lives under a government that openly intends to immediately establish a political system with completely worker-controlled industry and decentralised planned economy, regardless of the governmental and social policies
There does not need to be an official declaration of war, but it must involve some foreign troops, such as those deployed in overseas military bases on their territory, so purely funding a local coup or insurgency wouldn't count
The year timer for a given geopolitical sphere starts once the first/next nation within becomes communist according to the above definition, and includes the invasion of other nations within the same sphere that become communist within the same window
Some maps and infographics for context:
https://www.visualcapitalist.com/u-s-military-personnel-deployments-country/
https://www.reddit.com/r/MapPorn/comments/s9u1by/map_of_major_military_alliances_in_the_world/
1,000My current train of thought is that the major global powers themselves are likely too powerful for others to try to invade, but the smaller nations with significant foreign troop presence in particular are quite likely to be invaded immediately by the global powers for threatening the status quo if they ever do it ๐ค I'm by no means an expert though so feel free to correct me