Why does the UK have a Queen instead of a King?
- Why is that?
- Is it because this way you know that the blood line would be still okay or any other logical reason except for tradition?
To the downvoter: This is actually a good question, royalty has a tradition of male domination. If you do not like this, that does not make the question bad.
It all has to do with the line of succession to the British Throne. In the case of the current Queen, Elizabeth II, the story of how she became Heiress presumptive is described on Wikipedia:
During her grandfather’s reign, Elizabeth was third in the line of succession to the throne, behind her uncle Edward, Prince of Wales, and her father, the Duke of York. Although her birth generated public interest, she was not expected to become queen, as the Prince of Wales was still young and many assumed he would marry and have children of his own. In 1936, when her grandfather, George V, died and her uncle succeeded as Edward VIII, she became second in line to the throne after her father. Later that year, Edward abdicated after his proposed marriage to divorced socialite Wallis Simpson provoked a constitutional crisis. Elizabeth’s father became king, and she became heiress presumptive. If her parents had had a later son, she would have lost her position as first in line as her brother would have been heir apparent and above her in the line of succession.
And her ascension to the throne:
During 1951, George VI’s health declined and Elizabeth frequently stood in for him at public events. When she toured Canada and visited President Truman in Washington, D.C. in October 1951, her private secretary, Martin Charteris, carried a draft accession declaration for use if the King died while she was on tour. In early 1952, Elizabeth and Philip set out for a tour of Australia and New Zealand by way of Kenya. On 6 February 1952, they had just returned to their Kenyan home, Sagana Lodge, after a night spent at Treetops Hotel, when word arrived of the death of the King. Philip broke the news to the new queen. Martin Charteris asked her to choose a regnal name; she chose to remain Elizabeth, “of course”. She was proclaimed queen throughout her realms and the royal party hastily returned to the United Kingdom. She and the Duke of Edinburgh moved into Buckingham Palace.
@Relaxed it explains how the queen came to be (instead of there being a king) which I think is what the question is asking.