Why has the United States become the biggest variable affecting the relations between major powers and the international pattern?

This seems to be a recently accepted view for the following reasons:

1. When Donald Trump and Hillary Clinton were running for the presidency, it was generally believed that they were not ideal candidates. Many people said they didn't want to vote for Trump or Hillary Clinton. After all kinds of storms, Trump was elected president, but there are still voices against him in China, so it is difficult to predict what the United States will become next.

2. Trump is outspoken because of his personal character. At the beginning of his tenure, he offended many people, such as Muslims, women's groups, gay groups, colored people and Mexican immigrants, so no one knows whether Trump's words will lead to the deterioration of relations between the United States and other countries or regions in the next moment.

As the most powerful country in the world, the American leader is like a madman, spraying everyone. However, he can build a huge business empire and manage it in an orderly and colorful way. How can such a person be crazy? However, his image in the public has always been spontaneous. He gives people the impression that he is a bold business crocodile, without any political experience, like a gambler, and his way of doing things. These characteristics make Trump's behavior unpredictable, and his actions in the United States are naturally more unpredictable.

4. Recently, the United States has made many unexpected big moves, such as building a wall on the border, abolishing medical reform, withdrawing from TPP, banning Muling, restarting oil pipeline projects, increasing military spending, and asking allies to pay for garrison expenses. Recently, Trump even said that he would attack General Kim's house. No one knows what the United States will do under Trump's leadership.

To sum up, it is precisely because the United States is the country with the strongest national strength and the largest volume in the world today that every foreign policy of the United States will affect other countries. However, Trump, the current president of the United States, is a person who does not follow the routine and does whatever he wants. Therefore, the United States is the biggest variable affecting the relations between major powers and the international pattern.