The British monarchy lost most of its power in the Magna Carta in 01215, was interrupted by the establishment of the Commonwealth in 01649, was replaced by the Glorious Revolution in 01688, lost most of its remaining power to Parliament in 01689, and became British in 01707. I'll give you the Roman Empire, which lasted close to 1500 years, and also, for example, the Imamate of Oman, the Japanese Imperial Family (which has lost and regained its power over Japan two or three times), and Al-Azhar University, which celebrated its thousandth birthday about 50 years ago. There are a few other examples.
