FreeCol:Colopedia.concepts.independence.description/en

You start the game as an explorer with a handful of units at your disposal. The Monarch expects you to establish a colony in the New World and to bring treasures and exotic goods to your Home Port. You, however, have different plans: you wish to establish an independent nation. In order to declare independence, you need to convince at least 50% of the population of your colonies. You can do this by producing liberty bells, which also increase the efficiency of your colonies. As you can imagine, the Monarch will not just let you go. After declaring independence, you will have to fight and destroy the Royal Expeditionary Force (REF). If the REF ever controls all your coastal colonies, or at least 90% of your population, your bid for independence will fail.