Groups of nations signing treaties which pledge all to combat against other nation(s) who may have signed similar agreements has been used as short-term deterrent against any of those grouped nations being attacked or invaded. However, long-term such agreements bring greater risk to those nations when unavoidable conflicts break out between nation(s) of one pact versus nation(s) of another.
Instead of these formal pacts we desire the flexibility of defense training co-operatives where participating states plan and carry out in relatively short term joint military exercises while stating common defense and diplomatic, resource, territorial, etc. interests without formal clauses that automatically invoke associated states to war if one of theirs should come under attack. Thus when an associated state is brought into conflict the other states associated can each decide unilaterally on coming to that state's defense if deemed necessary. So small conflicts need not guarantee invocation of greater war.
Such an informal cooperative structure encourages associated nations to re-assess each other's status as allies more often and quicker without the constrictions of entangling alliances by treaties. It will also incentivize against associate nations dropping their defense postures and budgets while solely relying on the backs of more major players under their common treaty groups. Mutual and periodic joint saber-rattling is the more show-and-tell indicator of dedication from associates and of outward resolution against common foe(s).
In light of all this we would convert NATO into a more informal and flexible NAMTO - the North Atlantic Military Training Organization where the most formal agreements are the where's and when's of the associated states next joint military exercises. This structure will lead to stronger individual states with option to mutual combat, avoidance of wider-scale wars and the bravado of which will speak better to their common goals.