Why did the Japanese want to move first against the US?

Answer 1

The Japanese had not initially considered entering into any dispute with the US. Japan's activities were focused south and west across China.

But america placed a stranglehold on Japan, stopping it from having access to oil to heat homes, move industry, and feed people. It was coming to a head and even up to the day before Japan's attack on Pearl Harbour, The Japanese Ambassador in Washington was meeting with US officials, trying to get the embargoes lifted.

Realising they could not last further, Japan took the decision to make a risky first-strike against the american fleet based in Honolulu, sinking or disabling as many ships as possible, in order to give it greater chances of combating the stranglehold being held around Japan's borders.

Answer 2

When the Japanese expanded their war beyond China, they knew that the US would become involved and had a powerful navy. One of their first moves, therefore, had to be to reduce or eliminate the threat from the US Navy.