NATO did not use any military force to enlist these new members.
But you are beginning to understand my point: war for territory seems to be deeply repressed in the human psyche... and has compelled creation of ALL the greatest human empires.
The best way to avoid war against human aggression, therefore, is to deter potential enemies with overwhelming potential force AND evidence that you will use it if necessary.
Show weakness and you are inviting war... as Chamberlain did in Munich... and as we did in the chaotic flight from Afghanistan.