What was disarmament? why did nations begin to disarm?

Disarmament is the nations trying to come to an agreement to reduce their armed power such as number of soldiers and amount of weapons. It occurs in different stages such as wwi and wwii also during cold war.
The nations tried to carry out disarmament as the more weapon were built and carried the more likely war was to occur as there would be distrust among nations. It is also due to the fact that building up of military power requires a lot of capitals which could be a heavy burden to countries, when disarmament is carried out,the economic burden on military could be reduced.

Hope it helps and good luck! :)