Centenary of the Accession of Boris III as Tsar of Bulgaria (Bulgaria 2018)

Souvenir Sheet Centenary of the Accession of Boris III as Tsar of Bulgaria it reflects the thematic directions:

World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a global conflict between two coalitions: the Allies (or Entente) and the Central Powers. Main areas of conflict included Europe and the Middle East, as well as parts of Africa and the Asia-Pacific. There were important developments in weaponry including tanks, aircraft, artillery, machine guns, and chemical weapons. One of the deadliest conflicts in history, it resulted in an estimated 30 million military casualties, plus another 8 million civilian deaths from war-related causes and genocide. The movement of large numbers of people was a major factor in the deadly Spanish flu pandemic. 

A Royalty is the immediate family of a king or queen regnant, and sometimes his or her extended family. The term imperial family appropriately describes the family of an emperor or empress, and the term papal family describes the family of a pope, while the terms baronial family, comital family, ducal family, grand ducal family, or princely family are more appropriate to describe the relatives of a reigning baron, count, duke, grand duke, or prince. However, in common parlance members of any family which reigns by hereditary right are often referred to as royalty or "royals." It is also customary in some circles to refer to the extended relations of a deposed monarch and his or her descendants as a royal family. A dynasty is sometimes referred to as "the House of ...". As of July 2013, there are 26 active sovereign monarchies in the world who rule or reign over 43 countries in all