How did changing alliances in europe lead to the seven years wars and how was the war carried out on a global scale

France and Austria figured out that if they become allies, even though they were enemies for decades before, they could prevent Prussia and Britain from becoming stronger. Britain allied itself with Prussia to fight against them. It was fought on all continents using colonists. For example, the US colonies had to fight the Canadian colonies. African colonies also fought, and also Asian ones.