We have seen the German army after WW II here:
Afghanistan
I stand corrected.
Do you think Germany's involvement in Afghanistan bearing on the Christmas market attack?
No, this is too far fetched. There are 1001 (non) reasons why Germany is also a target for terrorism. And you know. It can't be avoided, reduced yes but not with totalirism methods. Safety is an illusion. If we forgoe our freedom for more big brother etc. and we break out in panic, the terrorists (no matter if left, right or islamic) achieve what they want. Most important thing is that we don't give them what they want - they all want to see fear. They want to see that we stop our democratic and liberal (not as cuss like some US people use it) freedom.
Germany also did see a nazi terrorist killing 9 people last year in Munich. That guy wanted to see the fear in the faces of the people, because he was on a revenge tour for his miserable life ...
Germany also saw 122 nazi arsonist terror attacks in 2015. Other sources say 94 nazi arsonist terror attacks and 8 nazi terror bomb attacks.
In 2016 Germany saw 66 nazi asronist terror attacks and 4 nazi terror bomb attacks.