Because you know, you need some place to bend all those tin cans, unless you plan on keeping them gathering dust and rust in some corner.
What IS the Battle of the Nations? Taking the name from that OTHER Battle of the Nations ,
its more or less an international medieval full contact combat tournament. Its not reenactment - more like LARP/SCA/WWF with swords and plate armor, but non the less - its pretty awesome in its own right. There are participating teams from half a dozen or more countries in several trials - 1 on 1, 5 on 5, full 21 on 21 etc.
There are teams from all over the world but the regulations and requirements are high.
For more info you can visit this Ukrainian site http://www.battleofthenations.com.ua/
It has english version as well.
You can also watch this short episode series on medievalists.net