Canada

that’s exactly why we’ve been stuck on an endless cycle of Liberal/Conservative governments for the last handful of decades

Genuinely I can't see how this follows and I've tried.

Keep in mind when I say ABC, I don't mean anything like campaigning for the LPC instead of the NDP "to defeat" the CPC. ABC in my world is just about strategy of voting on election day (or early voting), not about doing what you should do to get more people to vote for the candidates you want to win. If I prefer the NDP (I do), I'd donate and talk to friends and family about voting NDP, especially in the ridings where NDP candidates can win. For example in Parkdale—High Park, but not in Fort Mac.

By voting ABC I mean specifically looking at the numbers for the local riding on the day I vote, checking which one of these cases they resemble:

• CPC: 34, NDP: 33, LPC: 33
• CPC: 44, NDP: 44, LPC: 12
• CPC: 44, LPC: 44, NDP: 12
• CPC: 12, LPC: 44, NDP: 44
• CPC: 12, LPC: 48, NDP: 40

Then vote like this respectively:

• CPC: 34, NDP: 33, LPC: 33
  • Vote NDP since either has a chance of beating CPC and I prefer NDP
• CPC: 44, NDP: 44, LPC: 12
  • Vote NDP since they're the only ones that have a chance of beating CPC. Voting LPC likely won't get the LPC to win this riding but is depriving the NDP from a vote that can tip it over the CPC, therefore increasing the chance of the CPC winning
• CPC: 44, LPC: 44, NDP: 12
  • Vote LPC since they're the only ones that have a reasonable chance of beating CPC. Voting NDP likely won't get the NDP to win this riding but is depriving the LPC from a vote that can tip it over the CPC, therefore increasing the chance of the CPC winning
• CPC: 12, LPC: 44, NDP: 44
  • Vote NDP since the CPC has no chance of winning this riding and I prefer NDP
• CPC: 12, LPC: 48, NDP: 40
  • Vote NDP since the CPC has no chance of winning this riding and I prefer NDP and hopefully we can close the gap and defeat the LPC candidate

There are other cases, but these are good enough to illustrate my reasoning. I just can't see how this strategy can lead to more wins for CPC and LPC and fewer for NDP. ABC as described here should lead to fewer CPC MPs and more other MPs proportional to their vote share. Under these conditions, how much that vote share is depends on who people prefer more.

I think the reason why we've had CPC/LPC swings for decades has more to do with Canadian society as a whole eating up the neolib propaganda fed to the world since the 80s.