> * Intervention in the violent breakup of Yugoslavia, invited to do so by the UN in response to the genocide going on there.
Indeed. So not an aggressive invasion but a humanitarian intervention.
> * Invasion of Afghanistan, following the invocation of Article 5 after an attack on a NATO country (i.e., 9/11).
Not quite. Technically speaking, neither of the official NATO missions in Afghanistan, ISAF and Resolute Support, were Article 5 missions.
When the US triggered Article 5 in October 2001 it explicitly did not request a full NATO response, but initially only for support such as NATO AWACS aircraft in US airspace. When it invaded Afghanistan, which was entirely justified in international law as an act of self defence, a handful of NATO countries opted to send support contingents, like SOF, as a way of showing solidarity. But it was not a NATO mission under NATO command: Operation Enduring Freedom was American-led and commanded from the beginning. At best you can say several NATO allies invaded. Later, NATO launched ISAF and Resolute Support and became more involved as an organisation deploying forces, but that was post-invasion.
