Militarism is the ideology that military strength is the source of all security. In its mildest form it is often stated as many more specific arguments for military preparedness, all of which tend to assume that to achieve "peace through strength" is the most or only route to achieve peace.
Militarism tends to be defined in direct opposition to peace movements in modern times. Historically the term occurred with reference to specific states engaged in imperialism, e.g. Empire of Japan, British Empire, Third Reich, New Roman Empire of Mussolini, Union of Soviet Socialist Republics, Iraq under Saddam Hussein. Today it is often applied to the United Kingdom, Israel and the United States, and many of their opponents, e.g. North Korea and Syria.
Miltarism is sometimes contrasted with the concepts, mainly Chinese, of comprehensive national power and soft power and hard power. The current Chinese leadership believes that a strong China is necessary to national security, but that the military is only one component of national power, and that an excessive focus on the military may lead to less national power in areas such as the civilian economy.
One aspect of militarism is the ascendancy of a small clique of military officers to unchallenged power, as in Iraq, Third Reich and most of Latin America up until the 1980s. Nevertheless, although many militaristic states are military dictatorships, militarism is not synonymous with dictatorship or authoritarianism; liberal democracy and militarism are not mutually exclusive.
One way to measure militarism is the percentage of a country's GDP that is spent on the military. In 2001, North Korea had the highest expenditure of 31.3% of national GDP, followed by Angola (22% in 1999), Eritrea (19.8% in 2001), Saudi Arabia (13% in 2000), Ethiopia (12.6% in 2000), Oman (12.2% in 2001), Qatar (10% in 2000/2001), Israel (8.75% in 2002), Jordan (8.6% in 2001), and Maldives (8.6% in 2001). 
Another measure that has been commonly used is the number of military personnel per capita.