The reason for the teaching of Kalachakra is that "Nirvana is peace" is a good slogan, but in reality when you attain nirvana you enter a state of spiritual war, which is the subject of the Kalachakra tradition.
There is the inner spiritual war against one's own kleshas, and the outer spiritual war (which we don't attempt to define).
To some extent the spiritual war exists in the Mahayana sutras also, like The Great Parinirvana Scripture, where it is said that true bodhisattvas don't even take the five precepts so that they can take part in the war whose purpose is to protect the existence of the monastic sangha. It is no wonder that Mara himself gives his blessing and his mantra in the Great Parinirvana Sutra!
Atleast in Europe the name used to be Harmageddon and not Armageddon as it is nowadays. It was probably changed because Harma-geddon too obviously derives from Dharma-geddon, which leads us to think that it was borrowed from the Shambhala/ Kalachakra teaching at some unknown point in the past.
(ref. Charles Patton translation of the Mahaparinirvana Scripture)