It is an inevitability. Just like with the Lib Dems/Labor in the UK. Plurality first past the post systems always lead to two parties due to Duverger's law (http://en.wikipedia.org/wiki/Duverger%27s_law). If the right gets behind one party and the left splits the vote among two parties, the right will win again and again. Just look at Canada's 2011 election results. You think the conservatives aren't going to win again in Canada in 2015/2016 without a Liberal/NDP merger?
Did merging PC and Alliance automatically get them into government?
PR, yes. Instant run-off, no. If anything, IRV reinforces the two-party system further - see: Australia. Idiot.
