One of the selling propositions of expeditionary warfare is that expeditionary capabilities of armed forces protect weaker countries against aggressors.* The scenario usually goes like this:
Small country is being under attack or threatened -> some super-deployable notional force arrives on the scene -> ??? -> Success!
This isn't merely about intra-continental administrative marches as what I wrote a couple days ago: It's about massive budgets for airlift capacity, aerial tankers, amphibious warfare ships, aircraft carriers or even only about squeezing some army vehicle into some medium-sized cargo aircraft.
Strangely, interventions are rarely similar to their advertisements (quel surprise!).
Three kinds of case studies about the interventionist cause have become quite apparent during the last generation:
(1) Strategic offensive cases after months of undisturbed force build-up:
Iraq 1991, Iraq 2003
(2) Strategic defensive cases in which intervention forces aren't used at all or arrive very late:
Ruanda/Burundi 1994, TF Hawk 1999, South Ossetia/Georgia 2006, Ukraine/Crimea 2014
(3) Cases in which interventions began small and swelled up in size over time
Kosovo Air War 1999, Iraq occupation 2003-2007, Afghanistan 2001-OMG, Libya 2011
The very few flash-like interventions were meanwhile largely the business of the French and happened in Africa. The initial overthrow of the Taleban in 2011 with indigenous allies and few dozen Western soldiers on the ground supported by very long-range air power was another partial example.
The Ruanda/Burundi (or Hutu vs. Tutsi) genocide event of 1994 was an especially disturbing case, all interventionist bashing aside for once. Intelligence officers warned early about the potential for mass violence, but their warnings drowned in the noise of diplomatic cables and intelligence assessments. There were only weeks time to prevent the worst with an invasion, and the whole nightmare was completed within roughly a hundred days. The lag in understanding what's happening plus the lag of building political will to stop it and finally the landlocked location which required overflight rights and other details added to a very troublesome mixture.
The most irritating Rwandan Genocide is in my opinion the biggest challenge to the anti-interventionist cause.
An intervention in Rwanda wouldn't have required most of what interventionists demand for the armed forces, though. Interventionists argue for more budget, more aircraft, more ships, more brigades, bombings and invasions - they don't focus on building up politicians' cojones to intervene quickly and decisively where there's no ally, no oil, and no figurehead of evil.
*: And of course there's never a cost/benefit analysis attached. It's never with interventionist talking points.
P.S.: I admit; I ran out of good titles..