what were the causes of the japanese invasion in the philippines?

Answer 1

There were two causes -- one involving the Americans, and one involving Southeast Asia.

For several years, the Japanese had been waging war in China, and the U.S. didn't like it. As a deterrent or punitive measure, the U.S. cut off shipments of oil and steel to Japan. Since Japan was dependent on imports for its raw materials, it knew it had to get new sources of supply. Oil and rubber were available in Southeast Asia, so Japan determined it would strike south.

That would provoke the U.S., so Japan decided to try to knock out the American Pacific Fleet with a preemptive raid against the U.S. base at Pearl Harbor in Hawaii.

The Philippine Islands were an American possession, and there was a U.S. air base there (Clark Field), as well as a small naval base (Manila, I think).

The Philippines were right alongside the sea lanes between Japan and Southeast Asia, the intended target. So the Japanese decided that (a) they had to eliminate the American forces in the Philippines to protect their invasion route, and (b) they had to take over the Philippines as part of their defensive perimeter, allowing them free rein in the South China Sea.

The attacks against Pearl Harbor and the Philippines were simultaneous. Since the Pearl Harbor raid was only a foray, that happened and was over with. The Philippines were a much larger operation, involving ground troops, and it took some time before the American defenders were cornered and rounded up at Bataan and Corregidor.

The Japanese held the Philippines until late in the war when MacArthur famously returned. During the time Japan held the islands, their routes toward Southeast Asia were largely protected, although U.S. submarines operated there, and, after Midway and Guadalcanal, the U.S. was able to start the island-hopping campaign that ultimately led to Japan's defeat.