Here's one that I don't see mentioned very often:
-The WarGame series
A series of RTS military conflict games with multiple alternate history scenarios as their premise, allowing you to take control of either NATO or Warsaw Pact powers. They focus on the Cold War, looking at numerous points during that period where tensions between west and east could have escalated into conventional warfare. Each game has a campaign mode which explores these premises. The games are:
1. European Escalation (focusing on, obviously, Europe)
1975: East Germany aggressively demands that West Germany turn over defecting soldier Werner Weinhold. When the west refuses, East Germany invades the west, prompting NATO to intervene to defend West Germany, which turn prompts Soviet involvement in the German border skirmish
1981: When Wojciech Jaruzelski orders martial law in Poland as a response to the growing popularity of Lech Walesa's Solidarity, miners at the Wujek mines respond by going on strike. Jaruzelski sends in the army to break up the strike. The Polish army is backed by the rest of the Warsaw Pact, while the strikers get support from NATO. Eventually, Czechoslovakia follows Poland's example and defects to NATO, prompting a further escalation of the conflict.
1983: The Soviets misinterpret Able Archer as a genuine attempt by NATO to invade the USSR, and launch a preemptive strike, triggering WW3 when the Warsaw Pact invades West Germany.
1984: Following a nuclear war that has destroyed major cities in both NATO and Warsaw Pact powers, the political leaders of both sides call for peace. But a rogue Soviet commander who blames the politicians for starting the war begins leading an army to attack the peace conference
1979: When a NORAD technician runs an exercise on Soviet missile strike capabilities without leaving the computer in simulation mode, the USA mistakenly comes to believe that the Russians have launched an all-out nuclear strike. They order retaliation, only later realizing that the missiles haven't actually been launched. They abort their missile launches, but are too late to recall their conventional military strikes.
2. AirLand Battle
-The entire game focuses on a NATO/Warsaw Pact war breaking out in Europe in 1985. The main focus is on the conflict in Scandinavia, as both sides try to gain the upper hand.
3. Red Dragon (focusing on Asia)
1979: When Vietnam invades Cambodia in order to contain Chinese influence, China responds by breaking their alliance with the Soviets and invading Vietnam. The Soviets respond by building up their forces along the Chinese border and putting the pressure on the PRC to withdraw from Vietnam. Beijing concludes that they need to strike at the Soviet forces before they fully amass.
1984: Riding off the wave of victory in the Falklands, Margaret Thatcher, during a diplomatic visit to China, decides to say that Britain wants to keep Hong Kong, and calls for the renewal of the British lease over it. Deng Xiaoping refuses, and warns that China is willing to get the island back by force if necessary. Neither side backs down over this, both staking claim to Hong Kong. Finally, China launches an invasion of the island, with the local British garrison needing to hold its own while rallying the support of other Commonwealth forces.
1984: With relations between Japan and the Soviet Union at an all-time low due to the ongoing dispute over the Kuril Islands, Japan makes moves toward re-militarization, engaging in military exercises with the USA. When these exercises get too close to Vladivostok for Moscow's comfort, they decide that this is a precursor to an attack, and preemptively launch an invasion of Japan.
1987: South Korea is in turmoil as student protests against the Chun Doo-Hwan dictatorship turn violent. With the South Korean military distracted by domestic tensions and US troops ordered to stay in their barracks, North Korea decides that the time is ripe to invade the south and reunite the peninsula, pushing US and South Korean forces down to Busan.
1992: When the August 1991 coup in the Soviet Union is successful, the communists retain power in Russia. With their communist allies in Eastern Europe gone, the USSR turns to their Asian allies for support. They send military aid to China and North Korea, raising the concern of the UN and NATO forces and causing an escalated buildup of tensions in Asia. When the USS Enterprise is seemingly attacked in the Sea of Japan, it prompts a Second Korean War between all of the capitalist powers and communist powers.
Summary: These are some pretty intriguing and well-made games. But they have quite a learning curve. This is NOT Command & Conquer, and you have to relearn the rules of RTS games. Expect some frustrations when you first start playing and find yourself routed. But if you can get the hang of it, they're pretty good.