Belgium and the Netherlands? I don't think they have ever fought each other...of course I could be wrong there too.
Oh yes they have fought each other. In 1830, when Belgium seperated from the Netherlands. And they weren't as friendly to each other for over 100 years after; in 1919 it became nearly a war, because Belgium claimed that the German troops in WW1 had passed through NL (through the Southern part of Limburg), with Dutch consent when attacking Belgium. The Belgians conveniently forgot that 90 per cent of the Belgian refugees fled to NL. Also they claimed the Southern part of the province of Zeeland, which lies actually on Belgian soil, to secure the harbour of Antwerp. Only after pressure of the UK and the US, Belgium didn't invade the Southern parts of NL. In 1927 there was another crisis about a canal that the Belgians wanted to dig from Antwerp to the Rhine, which had to run over Dutch soil. NL opposed this very fiercely (leader of this opposition was the guy who later became the leader of the Dutch National Socialist Movement, the Dutch Nazis), but it was nipped in the bud and the canal has never been dug. Only in 1934, under the thread of Nazi Germany, the two small countries grew together to build a common defence against any future thread. Things went pretty fast after that, despite the interruption of WW2. In 1949 the BeNeLux was formed, blueprint for the EU.
M-G (and we still make jokes about the Belgians)