AFAIK anarcho-communists consider owning a private property as a violation of NAP. It implies that land also can not be owned. Thus if we consider anarcho-communists living on some territory, will they invade/conquer neighboring territories whenever they find it appropriate or beneficial to their communes?
To the best of my knowledge, the "Non-aggression principle" does not exist in any politically significant anarcho-communism.
The well respected and critical contribution, "You can't blow up a social relationship," ( https://libcom.org/library/YouCantBlowUpASocialRelationship8 ) puts the anarcho-communist view of violence in this way:
Libertarians look at history and at the ruling classes of the world and conclude that a libertarian movement will face state violence and armed struggle will be necessary in response. It is quite obvious that political activity could not even commence in certain conditions without taking up arms immediately. Also in certain conditions, as in peasant-based societies, it would be necessary to set up armed bases in the countryside. But the aim here would not be to carry out "exemplary" clashes with the military but to protect the political infrastructure to enable the spreading of ideas to continue. This may involve some guerrilla tactics but it cannot mean the strategy of guerrilla-ism. Nor can it mean the creation of a separate, hierarchical, military organization, which is not only anti-libertarian but is also vulnerable and inefficient.
Armed struggle means people would be killed and there is no getting away from the fact that violence threatens humanism. But libertarians would hope to preserve their humanism by ensuring that armed struggle would merely be an extension of a political movement whose main activity would be to spread ideas and build alternative organization.
On the basis of prominent anarcho-communist theory, there is no reason to suppose that violence would not be an adjunct to spreading collective political behaviours, but there are good reasons to suppose that violence would not be the central element of this.
In relation to the history of movements, voluntary collectivisation in the context of territorial violence has occurred (Spain), and involuntary collectivisation has also occurred (Free State, Ukraine).
"Land ownership" isn't the critical category in the territorial aspects of violence.