A lot of wars it did not really start; if you blame the US for Vietnam (instead of the french), you also have to count South Ossetia, Abkhazia, Transistria and Chechnya 1 & 2 on the Russian side.
The industrialized nations that actually did laudably little warmongering in the last half centuries are (somewhat ironically) the core WW2-axis powers: Italy, Austria, Germany, Japan; despite having plenty of "opportunities" to start something (e.g. over Königsberg/Silesia, Dalmatia, Kuril islands, ...)