Which entities' actions started the unraveling of the modern definition of sovereignty?

For Hobbes, sovereignty was a horrible conception, everything turns to the means of restriction, which allow the sovereign to issue rights and to dictate the laws in any way he pleases. The same idea also emerged as a reaction to the Holocaust of Second War Wolrd, a horror that leaders attributed in part to the lack of accountability of the sovereign State. Today, the European Union, as example, now links important aspects of its sovereignty to a "supranational" institution, where its freedom of action is limited and no longer absolutely sovereign. So, countries of European Union can't decide importan things without the approvation of others European Union members.