cowardice

They lacked the means to do so. It was kind of like a case of "too much ambition, not enough talent."

There is no way they could have pulled off such a large military operation.

There was no interest in invading the US mainland because that wasn't the aim of the Japanese. They were more interested in colonial expansion to China, but had been shut out by the Americans and Europeans, except for Manchuria. The Japanese were more interested in advancing their colonial interests in the Malay and Dutch East Indies. The American warships presented the only real threat to the Japanese expansion (and Americans had generally been the only country to oppose Japanese colonialism as the US (and US corporations) sought to expand themselves into China. The Malay area was rich in natural resources that the Japanese generally lack.

In more ancient times yes. When I think of Japan in WW2, this comes to mind: Japan's plan was simple, according to Robert C. Mikesh, a former Air Force officer who wrote the book "Japan's World War II Balloon Bomb Attacks on North America" (Smithsonian Institute Press, 1973): Launch balloons with incendiary and antipersonnel bombs attached, let them travel across the Pacific with the prevailing winds and drop them on American cities, forests and farmlands. This wasn't the work of Samurai's, but a power hungry dictator who used school aged children to manufacture these rice paper bombs. They had no military targets in mind, only civilian casualities.

Mainly because of geography. The US mainland is simply too far away from Japan.

I had an uncle that served with General McArthur and during the post war occupation. We did uncover detailed plans for the attack of the west coast. The objective wast to have been the ship building capability along with other industry west of the Rockys. With a few well placed bombs in the mountain passes, it could have been very difficult for the military to respond from the Eastern United States, especially since 2/3 of our overseas forces were in Europe fighting the Germans. Remember, at that time, most of the population of the US was east of the Rockys. The Japanese needed a base of operations to launch this Pacific Coast attack from. The plan was to take Midway and then Hawaii. Meanwhile, the United States was able to break the Japanese code and because of that were able to defeat the Japanese at Midway, despite being outnumbered 5 to 1. This battle turned the tide of the war and was the beginning of the end of the Japanese war machine. Most historians believe that the sheer scale of an invasion of the Western US would have been too much for the Japanese war machine and would have folded under its own weight. Also, the Japanese were concerned about the fact that most Americans were armed, but that would have not stood in their way due to their pride. And the prize could have been huge. Vast oil reserves and several shipyards existed at the time on our Pacific Coast. I have no doubt that we would have repelled any attempted Japanese invasion, but what a mess that would have been and how much longer would the war have lasted? Not to mention, it could have slowed down our attack on the Germans allowing them to finish their heavy water experiments first. Bottom line was that the Battle of Midway, was perhaps, the most important battle ever fought by the United States, and the reason we did not have to fight any battles on our mainland.

They thought it would be suicide or as Admiral Isoroku Yamamoto said. "You cannot invade the mainland United States. There would be a rifle behind every blade of grass." Makes me wonder now why so many are for gun control considering our second amendment was a great detterent to the US being invaded during WWII.

their fleet was all but destroyed at the battle of Midway