Why did the Japanese admiral Isoroku Yamamoto feel it was necessary to attack Pearl Harbor?

President Roosevelt Moved the pacific fleet from California to Pearl Harbor. This was a huge threat to japan who wanted to expand there dominance to the pacific. Japanese leaders saw a war between the US and Japan was probably gunna happen so they just said we should attack first. Yamamoto Isoroku planned the attack for months before and he wanted to crush American morale so they couldn't stop there advance across the pacific. This turned out pretty mad because US citizens where outraged and millitary enlistment went through the roof.