In WW1 The Central Powers we’re very effectively blockaded only engaging in one major battle, the Battle of Jutland between the Royal Navy and the Kriegsmarine that effectively ended in a draw. The blockade was very effective. In WW2 the Royal Navy still controlled the seas and the proposed invasion of the UK, Operation Sea Lion, would have been made up in large part of river barges to cross the channel. Their were serious doubts that they would be even up to the task of making this short but rather difficult crossing. After losing the Battle of Britain the plan was shelved and obviously never brought back. A transatlantic voyage was simply out of the question. The Japanese did land ~8,000 men in the remote Aleutian Islands of Alaska but this was at the very limit of their range and they were poorly supported. Eventually cut off from support from any surface vessels by the US navy. At no time in either war did the Axis or Central powers have even close to the ability to launch a cross ocean invasion due to the Royal and/or US navy. Look at what went into D-Day where you had the US, UK and by this time quite large Canadian navy all participating in the invasion with the staging ground of England less than 100 miles away from mainland Europe and it’s quite clear the incredible difficulty one faces launching a naval invasion.