At the following table from the Global Fire Power you can see the ranking of 126 countries according to their military power. I have only included the first 15, but you can see the rest of them in the article.
As you can read at the following article from Business Insider, titled “The 35 Most Powerful Militaries In The World”, July 2014, Global Fire Power is using over 50 factors in order to do this ranking every year. You can see that Germany has the 8th strongest army, lagging France and Russia, and Japan has the 9th strongest army in the world. However Japan has the 3rd largest economy in the world, and Germany has the 4th largest. Normally economic and military power go hand in hand. At the Business Insider article you can read that neither Germany nor Japan possess nuclear warheads. For Germany and Japan it has been a geopolitical choice to disconnect their military potency from their economic one. Actually this was initially enforced upon them, after the end of World War 2, and gradually it became their own choice.
The Germans decided to constraint their military power in order to stop being a threat for the French and the Russians. These three countries are sitting on the flat geographic corridor that runs from France to Russia, avoiding the Alps and the Carpathian Mountains. There are not many physical barriers in this geographic corridor. Napoleon used this corridor in 1812 to lead the French army to Russia, and Hitler used this corridor to lead the German army to Russia in 1941. Therefore France is afraid of Germany, Russia is afraid of Germany, and Germany is afraid of both. See map 2.
The Germans and the Japanese are very disciplined people and very talented in creating industrial miracles. Both of them experienced extreme industrialization in the 19th and 20th centuries, and both of them were very poor in raw materials. They both had to struggle with the traditional powers for the control of the resources they needed for their industrial machines.
There was a lot of tension between Germany and France for the rich in coal and iron fields of Alsace and Lorraine, and of the Ruhr valley and the region of Saar, all regions between France and Germany. With the Franco-German war of 1871 the Germans took control of these regions, and the French took them back after the First World War in 1918, but Adolf Hitler took them back again during the Second World War, when he invaded Germany in 1940. After the end of the Second World War, actually in 1951, the European Coal and Steel Community was created. The ECSC created a common market for coal and steel, in order to prevent Germany and France from going to another war.
However a few decades ago, at the end of the 19th century, the Germans were trying to build a navy which would allow them to challenge the French and the English for the resources of Africa. The Germans had also agreed with the Ottomans to construct the Baghdad Railway which would connect Berlin to the Persian Gulf, providing the Germans with access to the oil of the Persian Gulf. For some people the Baghdad Railway was the main cause of the First World War.
Besides it is not a coincidence that before invading Poland in September 1939, which was the beginning of World War 2, Adolf Hitler agreed with the Russian communists that they would provide the Nazis with oil, iron and grains (Molotov-Ribbentrop Pact of 1939), in return for Germany manufactured goods. The pact was signed in August 1939, and once Hitler had secured his eastern borders and his supplies in raw materials, he invaded Poland on September 1st 1939.
In the meantime Japan was facing a similar to Germany’s situation in the Pacific Ocean. Japan was the rising industrial power, and she had to compete with the Americans and the Europeans who controlled the resources of the Pacific and the Indian Oceans. There was therefore tension between Japan and the US, and that was a major problem for the Japanese, because the Americans were their major supplier in oil. In 1931 the Japanese invaded China through the Korean peninsula and annexed the rich in resources Manchuria, which further increased tensions with the Americans, who were Chinese allies. But that was not enough for the Japanese, who also invaded the French Indochina, which today is Vietnam and Laos (see yellow circle at the following map).
The United States imposed Japan an embargo on the sale of oil, and the Japanese believing that a war with the US was inevitable, decided to attack Pearl Harbor, in order to destroy the American navy of the Pacific Ocean. Then the Japanese annexed the Philippines, which was controlled by the Americans, and the rich in oil Indonesia, which was controlled by the Neitherlands. Today Indonesia is the 30th richest country in the world in terms of oil reserves, but at the time Indonesia was even richer, because at the time many of today’s known oil fields had not been discovered yet. Japan almost managed to invade Australia.
At the following map of Wikipedia you can see that by 1942 the Germans and the Japanese were very close of taking control of the oil of the Middle East and the Caspian Sea, which would seal their victory in Europe, Asia and Africa. But this never happened as the British defeated the Nazis at El Alamein in 1942, and the Russians defeated the Nazis at Stalingrad in 1943.
At the end of WW2 both Germany and Japan were completely destroyed. Germany was destroyed by the Americans and the Russians, and Japan was destroyed by the Americans. In Japan, where the Japanese would not surrender, and it was estimated that hundreds of thousands of American soldiers would have to die before Japan surrendered, the Americans dropped an atomic bomb. Japan did not surrender, and the Americans dropped a second atomic bomb, which led to Japan’s unconditional surrender.
The two allies, Germany and Japan, never forgot what happened in WW2, and they prefer to constraint their military potency. Germany wants that for not being a threat to France and Russia, and Japan for not being a threat to America. However for the US today it is better if Japan becomes stronger, because together they are trying to prevent China from converting the South China Sea to a Chinese lake, by militarizing the islets which are located in the exclusive economic zone of the other countries. Moreover Japan and China have differences over the Shenkaku Islands in the East China Sea, and Japan and Russia have differences over the Kuril Islands in the Sea of Okhotsk. But if Japan becomes too strong China and Russia will not be very happy.
For Germany things are a bit more complicated even though Germany is a NATO member. The thing is that Germany has very close cooperation with Russia. Germany is the number one importer of Russian oil and natural gas, and Russia is a major importer of German manufactured goods. It seems that it is France which has the stronger motives to align her foreign policy with the US. A stronger Germany would make France feeling uncomfortable. England would not feel very comfortable either, because England feels that the European Union threatens the City of London as the major European financial market.
For the Global Fire Power article see
“The complete Global Firepower list puts the military powers of the world into full perspective”, August 2015
For the Business Insider article see “The 35 Most Powerful Militaries In The World”, July 2014