Why did Johnson need the Queen's authorization to become the British Prime Minister?

Because this is a British institutional requirement, the institutional characteristics of each country are different. Boris Johnson, leader of the ruling Conservative Party in Britain, officially took office as British Prime Minister on 24th. On the same day, at Buckingham Palace, Theresa May submitted her resignation to Queen Elizabeth II and was approved to step down as British Prime Minister. Subsequently, Johnson accepted the Queen's authorization to form a new cabinet and officially became the British Prime Minister. Due to the current national system in Britain, the British Prime Minister must be authorized by the Queen to take office.

In Britain, the prime minister is equivalent to the executor of the queen system. Britain is a constitutional monarchy. In state power, the queen usually does not participate in politics, but every decision needs her signature. As far as state power is concerned, the power of the British Prime Minister and Parliament is definitely greater than that of the Queen of England, but this does not mean that the Queen has no power. In Britain, the queen is above the law. Besides, the British Parliament is the highest authority in Britain, and the Queen can dissolve Parliament unconditionally, which is her power. Every prime minister takes office, although they are all elected by everyone, but they need to be canonized by the queen before they can be formally appointed.

Britain is a constitutional monarchy, and the Queen of England is equivalent to the Prime Minister of Japan. Strictly speaking, the Queen has the right to dismiss any official in the Commonwealth, even the Prime Minister, but she never uses these rights. The relationship between the Queen of England and the Prime Minister is different from that between the emperor and the Prime Minister in China. After all, the emperor of China wanted to participate in politics directly.

The emperor of Japan used to have high power, but now, the emperor has gradually become a position without real power, and the whole royal family has no real rights except as a symbol of a country. The Prime Minister of Japan, that is, the Prime Minister of the Cabinet, is actually the leader of the ruling party and a person who holds real power.