Germany and Japan were both hoping to expand their boundaries at a time when the world was isolationist and hoping to avoid the horrors of the First World War. Japan was impressed with Germany’s ability to dishonour treaties and take over countries (Austria, Czechoslovakia) without triggering an international war. Germany was impressed with Japan’s expansion in Manchuria and hoped to persuade the Japanese to fight against the Soviet Union (thus having a two front war in the East) as well as the Americans should they be drawn into the war.
The problem with Japan was that in order to secure what they had, they needed just a little more. Namely some strategic supplies that were not available in the lands they held in 1941, specially oil. To “stay out of WW2” would have meant for Japan to back off on some of what was already conquered, as the Western powers with interests in Asia – Britain, the USA, the Dutch government-in-exile (Indonesia) – had drawn the “line in the water” and imposed sanctions on Japan. So they gambled on being able to land one mighty first blow that would leave all of SE Asia and the Western Pacific open to takeover before anyone could regroup.
The lack of a declaration of war didn’t keep the Japanese from fighting the Russians on and off prior to and during WW2. There was a constant state of tension throughout this period between both nations, with almost constant border incidents, frequent cross-border clashes and a number of major battles, largely driven by Japanese expansionism. The Russians finally formally declared war on Japan just before the Japanese surrender.
Right - the bomb was dropped on Hiroshima on Aug 6, and the Soviets declared war on Japan on Aug 8. Interestingly enough, a peace treaty was never signed between Japan and the former Soviet Union. So technically, they are still at war.
The attack on Pearl Harbor was indeed extremely desperate, but Japan’s clash with the U.S. seemed inevitable. Japan’s expansion in the Pacific Rim conflicted with American interests there. Also, as another poster mentioned, the embargoes (oil, metals) were crippling Japan. The terms for lifting the embargo were that Japan should withdraw from China. Japan attempted to negotiate a partial withdrawal, but the answer was - all or nothing. The attack on Pearl Harbor was a preemptive strike to weaken the U.S.'s Pacific fleet, thus giving Japan some breathing room in which it could grab resources.
It was either
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Play a desperate gamble, attack the U.S., and possibly gain enough resources to continue a war or scare the U.S. into staying out of the Pacific, or
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Withdraw from China and give up its empire. At the time, Japan’s biggest fear was becoming an Asian colony of some Western power, plus, pride and arrogance wouldn’t allow it to give up any territory. So, choice #1 seemed the only choice, given the path they chose.
I’ve only just been told I mucked up the spelling of lebensraum. That’ll teach me t’ got check the references before posting a foreign word. 