Just recently, Donald Trump admitted that Jerusalem was the capital of Israel. His historic decision ignited a broad criticism internationally.
Previously, the US had an opinion that the stance of Jerusalem was under discussion. But, in 1995, an act regarding Jerusalem embassy was established. It demanded the government to move the embassy to Jerusalem.
However, considering a complicated situation around Jerusalem, each administration in the US delayed enforcing this act. Clinton,
Bush, and Obama decided to postpone the movement of the embassy. As a result, this act has been negated for over 20 years.
Donald Trump had declared to enforce this act since he was a candidate for the Presidential vote. Thus, his commitment is consistent with his original policy.
However, it is not sure why Trump began to move in this moment. Some people believe Trump attempts to deflect criticism from his domestic policy by attracting public attention to the international relationship.
But, I do not agree with this idea. Trump might predict that his decision would ignite a serious argument. Indeed, the UN committed that the US' declaration was null and void by the vote of 128-9. Trump had threatened the nations which were supportive of the UN's commitment. If he had utilized this issue as a smokescreen to domestic criticism, he would not have been conflictive so seriously. I guess he is motivated by his own ideology.
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Anyway, Trump's decision will make the situation worse, I am afraid. The current situation around the Middle East is so delicate that any particular nation cannot fix the issue.