Adrug is one which precedes the use of illegal or illicit drugs

A Gateway drug is one which one precedes the use of illegal or illicit drugs.

Gateway drug its means Habit forming drug that, while not itself addictive, may lead to the use of other addictive drugs.

"many believe that alcohol and cigarettes are gateway drugs that increase the risk of subsequent involvement with illegal drugs"

Gateway drugs it is a noun.

D. Nationalism is no longer the powerful force it was in the past

Explanation:

The Nationalism can be defined as identification with one's own nation, supporting its interests, protecting its culture and traditions. There are numerous things about the Nationalism that can be defined as good or bad.

The positive aspects of the Nationalism can be seen in the protection of a certain ethnic group, its culture, as well as cherishing the traditions, thus making sure they continue to exist.

The negative aspects of Nationalism emerge when it starts to take up more extreme form, so other ethnic and racial groups are neglected, persecuted, and even murdered. This has led to numerous genocides and ethnic cleansing around the world.

Lot of countries around the world have broken apart because of the Nationalism, as multiple different ethnic groups that were living in the same borders wanted and managed to become independent.

Even in modern times, the Nationalism is still very strong in most of the world, and in some countries it borders Nazism. Some that someone would not expect them to be, like in Greece where no other ethnic group (except the Turkish because of the enormous pressure) is recognized to exist and the people do not have their minority rights, but instead are often pressured or even attacked.