If you include the 7 years war, which was indeed a globally spread conflict, there have been 3. After all, the 14-18 war, ( or 17-18 if you are American ), was commonly named the Great War at the time.
Extreme hypothetical example;
Party #1 wins 51% of the vote in 326 seats, 0% in the others. Wins majority with slightly over 25% of the vote.
Party #2 wins 0% of the vote in those 326 seats, 51% of the vote in the others. Wins slightly under 25% of the vote.
Party #3 wins 49% of the vote in all 650 seats - gains no seats.
Not if you intend to vote Green in a safe Tory seat. For a large proportion of the seats in a GE the result can be predicted with a great degree of certainty.
Of course it does, second ( or third ) placed votes only serve to reduce the winning majority, none of those voters get any level of the representation they desired.
If you are in a safe Surrey Tory seat, how does a vote for the Greens count ? How do the almost 60% of votes cast, that went against the Tories, register in Parliament ? In theory a party could get 49% of the vote and gain 0 seats.
Democracy is supposed to be the will of the people, not of areas of land. Has any UK Government in the last hundred years had a majority of the votes cast, let alone a majority of the electorate ? Certainly not Blair or Thatcher with their 100+ majorities in the HoC.