Conscription

Conscription, also called draft, is when a government forces people to enlist in the army or other military service. Usually, only men are conscripted, but in some countries such as Israel, Norway and Sweden, women are as well. A soldier who has been drafted to serve in the army is called a "conscript". 
Conscription may or may not be compulsory. If compulsory, it may be resisted. Usually, exceptions are allowed. Since men in their late teens and twenties are the main objective, conscription clashes with higher education, and exceptions may be allowed.
The first large, modern conscript army was the French Grand Army after the French Revolution. Conscription soon became a common way of making up the armies. Almost all of the powerful armies in the world except United Kingdom were conscript armies, but during the World Wars, even the British Army used mostly conscripts.
Conscription was introduced in August 1916 in New Zealand during the First World War because the number of men needed to be recruited had not been met. 
Problems.
Conscription armies are large, but they are often poorly equipped and trained and have poor morale. In combat they usually suffer many casualties. Usually conscripts serve with little pay. Conscription may be considered as a type of forced labour. In some countries, young men who refuse to join the army are sentenced to prison. Many people "dodged" or illegally avoided conscription during the Vietnam War in the United States.
There are arguments for conscription. Some see it as fair since everyone shares the burden of service. A small country with few people can make up a large enough army by conscription. If a country is in the middleof hostile neighbours and war can break up at any time, or if the country is a "buffer state" (between two military powers), training all available young people as soldiers can be a good idea.
The alternatives for conscription are militia or universal conscription systems, as in Switzerland, or a professional army made up from volunteers. The United States gave up conscription during the Cold War. The Vietnam War proved so unpopular that the US Army no longer wanted conscripts, but volunteers, who have better motivation to serve. Most other Western countries followed the American example and gave up conscription. Some countries now have an all-volunteer army, and in Europe, universal conscription remains only in some countries like Finland, Russia and Turkey.
In Germany, conscription for the Bundeswehr was removed in July 2011 after a long discussion in the German Bundestag.
People who oppose conscription because of pacifism idea are called conscientious objectors. Some countries draft conscientious objectors but give them jobs in which they will not have to fight.