Luck

From EU3 Wiki

When a new game is started, 8 semi-randomly chosen AI-controlled countries are set to be "lucky". This is designed to create "Major Powers" in every game.

A lucky country gets the following bonuses (from static_modifiers, version 1.1) :

merchant_compete_chance = 0.1
colonist_placement_chance = 0.1
missionary_placement_chance = 0.1
leader_fire = 1
leader_shock = 1
land_tech_cost_modifier = -0.02
trade_tech_cost_modifier = -0.02
naval_tech_cost_modifier = -0.02
government_tech_cost_modifier = -0.02
production_tech_cost_modifier = -0.02
spy_efficiency = 0.05

When lucky countries are destroyed the game assigns another country to become lucky, so there will always be 8 lucky countries at all times.