I think this song's about someone who was suddenly pursued by a person that she didn't want to give in to, whether because she wasn't looking for a relationship, didn't like him, or whatever. Like a in a battles in a war, she put up a fight and tried to resist and get away from him, but in the end, gives in and "loses", ("...I tried to hold you back but you were stronger") proclaiming her "Waterloo", just like Napoleon finally lost at Waterloo. And along with proclaiming her defeat, she also proclaims her loyalty and love for the guy, who earned it by "winning" the war ("...I was defeated, you won the war... Promise to love you for ever more").
I think this song's about someone who was suddenly pursued by a person that she didn't want to give in to, whether because she wasn't looking for a relationship, didn't like him, or whatever. Like a in a battles in a war, she put up a fight and tried to resist and get away from him, but in the end, gives in and "loses", ("...I tried to hold you back but you were stronger") proclaiming her "Waterloo", just like Napoleon finally lost at Waterloo. And along with proclaiming her defeat, she also proclaims her loyalty and love for the guy, who earned it by "winning" the war ("...I was defeated, you won the war... Promise to love you for ever more").