I have had this idea for well over a year
Set in 2014 The story is about a new World War. Russia's government have been overthrown by a fascist dictator. Their first goal is retaking their old satellite states, though they do not try invading Scandinavia, because they learned their lesson last time. They have made quite a bit of headway, with much resistance from the European Union. The last line of defense for Europe is Kiev, which is nearly surrounded by Russian Forces. Britain is embroiled in a bitter civil war, with Northern Ireland, Scotland, and Wales fighting for total independence.
Relations between the U.S. and China are very strained. Communism is stronger in China then ever, with an extremist leader at the helm. North and South Korea are near war, as well. With the war in the Middle East past them, and the economy recovering well, things are going well. They are minimally involved with the Russia situation, with small battalions fighting in Kiev.
Then, everything goes to hell.
A nuclear strike lands off the coast of San Fransisco. It is unknown who exactly launched the nuke, but it no longer matters. The U.S. declares war on both North Korea and China. South Korea joins the U.S., and North Korea and China ally.
The gameplay would be first-person shooter, but the sheer depth would be immense, with many different campaigns. An American, European, Russian, Chinese, South Korean, North Korean, England, Defectors (Scotland, Wales and Northern Ireland),"Resistance" and Mercenary campaign, and that's just single player. Resistance players would pick between Russia, China, Europe, America, and the Korea's, and then fight with guerrilla tactics against those countries in their own land. Mercenary players would fight for who ever they want. They could choose to join a military contracting company, or go solo. Contractors would get more funds and start with better weapons, but get less of a choice of missions. Solo's have less money, has to supply their own equipment, but gets a bigger choice of mission. Mercenary missions would be more "behind the scenes" like missions with things like sabotaging and assassinations.
The American campaign follows a soldier fighting in the heart of China. European campaign follows a Ukrainian soldier drafted into a special forces-esque team from various European nations, fighting behind enemy lines in Russia. The Russian Campaign follows a Russian soldier fighting through Eastern Europe. The Chinese campaign follows a Chinese Soldier defending his home country. North an South Korean campaigns would both be fighting for control of the Korean peninsula.
When you start each campaign, you choose a soldier class. This class determines your equipment load out, mission objectives, and the way certain squad mates act around you. For example, choosing the Sniper class may have you teamed up with another sniper, providing support for the ground assault, while choosing the Support Class has you being part of the ground assault.
That's all I have right now. Suggestions?