the fact it is on an island.
Japans attack on Pearl Harbor, Hawaii
When Japan opened some if its ports to foreign trade their long history of isolation ended. So basically, their isolation (or Japanese isolationism) is what ended.
There wasnt a battle that ended japans threat, inface U.S.A was losing but the two nuclear bombs in Hiroshima and nagasaki ended the Japanese threat.
United States, i believe
isolation
isolation
Portugal
The US stopped Japans isolation in the 1800's by direct military action. The new Japanese government then went about westernising Japan. Ironically US intervention in 1800's Japan, lead to WWII.
Japans natural resources are the ocean, the forest, and farming
Japan
The Crusades and the start of exploration.