Have any Western countries come close to civil war in the last few decades?

If by 'last few decades' you include the '40s, then Italy after 1943 would probably fit the description.

The country's South was controlled by the Allies; the Co-Belligerant Italian Army fought along them against the Germans as well as the other fellow Italians from the R.S.I...
Mussolini was freed by the Germans and then put in charge of the Italian Social Republic, a puppet state with nominal control over the country's North and Centre; its armed branch had become, after the suppression of the M.V.S.N. (Fascist militia), the G.N.R. or Guardia Nazionale Repubblicana - whose members, the repubblichini, fought against the partisans and the other Italians from the Co-Belligerent Army.
The partisans, which were very active in the north and fought against both the Germans and the repubblichini.

So yes - I'd argue that between 1943 and 1945, our country was definitely in a state of civil war,

In 1946, Italy became a republic after a rather controversial referendum which was allegedly mirred in irregularities - a number of pro-monarchy rallies were forcibly dispersed both during and after the referendum had taken place (an example would be the massacre in Naples' via Medina, on 11 June 1946; protesters were fired upon and there were nine dead). The new King, Umberto II, chose not to dispute the referendum's results and joined the rest of his family in Portugal a few days later, so as to avoid further bloodshed.