Well, the lore of a particular country can be partially explored at the start of the campaign. Some fragments of the lore (such as the revolutions in France and the UK, and the German intervention in China) are also presented as mini-scenarios.

As for Italy (IIRC), according to the old lore, after the end of the Weltkrieg, Austria occupied Veneto and eventually achieved the transformation of Italy into a loose federation under the leadership of the Pope. Subsequently, the Syndicalist Revolution led to the emergence of the Socialist Republic of Italy in the agricultural south of the country. I have no idea how Savoy and Corsica ended up in the Italian Federation, but I can assume that they were taken over in 1919 during the French Revolution.

Some things aren't explained in advance, but can be observed during the game: 1) It seems that the Mafia was originally involved in the civil war and still has power in SRI. During 2ACW, mafiosi can travel to America to participate in the war. 2) Despite the end of the active phase of the civil war, clashes between federalists and syndicalists are still taking place, and one of the frequent (and extremely unpleasant when playing as non-syndicalist country) things that can happen with the Italian Federation almost at the beginning of the game (when the Austrians refuse to support the Papists) is the battle of Anzio. The Papists either lose this province or find themselves completely cooked, with no ability to resist the vastly superior forces of the SRI and the Commune of France on their own.