Rise of Nations lets you pick between "consensus" (Republic, Democracy and Capitalism :agony:) and "totalitarian" (Despotism, Monarchy and Socialism) governments, which give you different bonuses. This is how the game describes both:

"Consensus governments are dedicated to the economical and scientific development of a nation. Their Patriots offer production and defense bonuses and provide healing to nearby units and buildings."

"Totalitarian governments are devoted to military development and warfare, benefiting nations fielding lots of units and often waging wars. Their Patriots are oriented to offensive warfare and always give the benefits of a Supply Wagon (eliminate attrition and provide supply for artillery units)."