A constitution is a nation's plan of government. The Japanese and United States constitutions are similar because Japan's current plan of government dates from 1947, a time when Japan was occupied by U.S. military forces. U.S. military personnel, including Gen. Douglas MacArthur, wrote a new constitution for Japan at this time, using the U.S. Constitution as a model. However, the two constitutions also have major differences.
The first chapter of the Japanese Constitution describes the role of the emperor in Japanese society. The emperor has powers of state but not powers of government, meaning that he represents the country but has no lawmaking authority. There is no comparable office in the U.S. system of government. The president has both powers of state and government, and he is not analogous to an emperor since he is elected to the position he holds.
Renunciation of War
The second chapter of the Japanese Constitution contains a declaration that the Japanese people "forever renounce war as a sovereign right of the nation." In addition, the document promises that Japan will never use force or the threat of force to settle international disputes. To uphold this promise, the Japanese Constitution also promises that no armed forces will ever be maintained by the nation of Japan.
The U.S. Constitution contains no comparable statement. The only reference to war in the U.S. Constitution contemplate the use of it: Congress is empowered to declare war in Article I, Section 8. The U.S. Constitution also clearly contemplates the existence of armed forces for the nation, since Article II, Section 2 states that "The President shall be Commander in Chief of the Army and Navy of the United States."
Branches of Government
The Japanese and U.S. constitutions both set forth three branches of government, but these branches differ in the details. Japan follows a parliamentary system in which the people elect the legislative branch, called the Diet, and the Diet in turn selects the prime minister. In contrast, the leader of the United States is a president, not a prime minister; the president is elected by the Electoral College, which is composed of electors selected in each state. The national legislative branch, which is the U.S. Congress, has no role in selecting the president.
The Japanese Constitution, like the U.S. Constitution, can be amended, but the process is different. In the United States, the people have no direct vote on constitutional amendments. Instead, two-thirds of Congress and three-fourths of state legislatures must agree to an amendment. In Japan, if two-thirds of the Diet agrees to an amendment, it is brought before the people in a special election. If a simple majority of the people approve of the amendment, it becomes a permanent part of the Japanese Constitution.