I hear this brave maratha & marathi theory on the chat forms around from sometime now but I never had any time to study from a neutral perspective other than the 1 sided views of hindus.
If Maratha's were brave that was really good for them and I respect them if they were brave & were fighting for the just cause.
But I give you a little hint of as to why Sri Guru Gobind Singh Ji's was is Naded, read this one ..
http://en.wikipedia.org/wiki/Banda_Bahadur
and also try to read some articles other than generated by the hindu mind sets on other communities at times.
