I always see Luxembourg on maps of the Belgian invasion in WW1, and wonder why the Germans didn't sent their military through there. It seems like it would have avoided bringing in the British into the war, and likely would have been easier to push through. Why was Belgium a better option for the Germans to invade through than Luxembourg?
The short answer is that they did. Luxembourg had been guaranteed as a neutral state in 1867 when it separated from the Netherlands, so much like Belgium it had international protection in theory. Luxembourg is also tiny and by itself wouldn't permit a very broad front on France's north. Nevertheless, when the invasion started, Germans came through Belgium and Luxembourg, and Luxembourg remained under German occupation until the end of the war.