[drauz]

I see that my link to the wiki article failed, so here are some relevant extracts...
Germany:
"Before the winter of 1941, Germany appeared to be moving toward a swift victory over the Soviet Union in Operation Barbarossa. Alfred Rosenberg, Reich Comissaire for Eastern Affairs, was ordered to print the motto "Deutschland Weltreich" (German World Empire),[citation needed] and Hitler made known his intention of further conquest following victory over Russia. These plans appeared to include an invasion of the United States.

In Autumn of 1940, the attack on the US was fixed for the long-term future. This appears in Luftwaffe (German airforce) documents, one of which dated October 29, 1940 mentions the "extraordinary interest of Mein Führer in the occupation of the Atlantic Islands. In line with this interest...with the cooperation of Spain is the seizure of Gibraltar and Spanish and Portuguese islands, along other operations in the North Atlantic."

In July 1941, the Führer ordered the continued planning for an attack against the United States. Five months later, on December 11, 1941 Germany declared war on the United States.

Operation Barbarossa was alleged by some to be a testing ground for an invasion of America. Another alleged German invasion plan was "Operation Felix", in conjunction with Spain, which called for obtaining control of Atlantic islands and seas to launch long-range strikes and an eventual invasion of America.
Operation Felix (Fall Felix) and Operation Sealion, planned the occupation of Ireland and Operation Ikarus, would have provided some support bases for installing the Wehrmacht and Kriegsmarine infantry seaborne or Luftwaffe Airborne forces for the invasion.

These units, with proper support from the Kriegsmarine and Luftwaffe, were to capture coastal areas in Maine, New Hampshire, Massachusetts, Connecticut, Rhode Island, New York, New Jersey and Delaware.

On the other hand, the invasion could have come from airborne landings on the Atlantic coast of Canada in the Northwest Territories, Quebec, Newfoundland, New Brunswick and Prince Edward Island, with the army then continuing into U.S territory. The Saint Lawrence River was also considered to be a major possible entry point into North America. Another option involved launching seaborne rockets, long range missiles or aerial bombardments, against U.S. territory. The Germans were also considering the development and use of an atomic bomb against the United States.

Air strikes with heavy long range bombers would have not only put the coastal targets of New Jersey, Pennsylvania, Washington, D.C., Boston, and New York within range, but also targets in Ohio and even Indiana."

Japan:
"During the Second World War the Japanese Navy strongly advocated the capture of the Hawaiian Islands. This would have involved landing after the first stage of the war. The Hawaiian Islands could be used for future landings in the continental U.S., or to conduct aerial surface, naval, or submarine attacks against U.S. coasts. The operations bureaus of both the Army and the Navy investigated the matter on a number of occasions. When it became apparent that the Hawaii operation was beyond the capability of the Army to carry out alone, the General Staff vigorously resisted the project, which was eventually discarded.

Kinoaki Matsuo, a high-ranking officer of the Black Dragon Society, and Japanese Navy thinker wrote the book The Three Power Alliance And The United States-Japanese War, which is purported to detail the Japanese war plans for the simultaneous invasions of the Panama Canal Zone, Alaska, California, and Washington.

For Japanese Naval strategists, an invasion of American, Mexican, and Central American Pacific coasts would have required naval bases in the Aleutian and Hawaiian islands, as well as the Mexican Revillagigedo and French Clipperton islands.

From the Aleutians, Japanese forces would have landed in Alaska and Canada, from Hawaii naval or airborne landings in Washington state, Oregon, and California were considered. From these bases, long-range heavy land-based bombers or flying boat attacks on U.S. territory could be launched. The High Command staff considered bombing San Francisco, Panama, Los Angeles, the Texas oilfields, in coordination with German naval strikes against Boston, Washington D.C. or New York. The use of biological and chemical weapons was also considered."

It is also worth recalling that the German invasion of Britain (Operation Sea Lion, and note: "...the losses in personnel and materiel suffered by German paratroopers during the Battle of the Netherlands, in May 1940, could not be replaced in time for the planned operation.") may well have been successful had it been launched big and early in the war, despite Germany's weakness as a naval power... and America's invasion of the Japanese home islands could have failed, had it been required.