A succession of rulers related by blood is called a dynasty. In European nations, a dynasty is sometimes called a house. The great houses of Europe were often related to other houses by marriage, as intermarriage was a means of forging alliances, expanding power and securing territorial gain.
The early part of the 20th century was a watershed time in monarchical and dynastic history. The series of Chinese dynasties that ruled China for thousands of years ceased in 1912 with the end of the Qing Dynasty and the advent of republican rule. The First World War was precipitated by conflict between European houses, but at the conclusion of the war in 1918, only the British monarchy remained. Modern royal families are descended from the rule of houses and dynasties, but the power of the current houses of Europe is largely titular and symbolic due to a changed political landscape typified by constitutional and democratic rule.