I got some queries...My answers....

You write:
If Hindus follow and pray to God/s very sincerely with all rituals etc., how is it they are not rewarded prosperity...


My perception:
I dont think that the reward of Spirituality is in terms of prosperity gain...sometimes maybe, but not always...


You write:

Considering India as the origin of culture and philosophy, how come we were ruled for over 1000 years--is it not shameful to bear slavery for ten centuries...

My perception:
Yes you may be right...sometimes it is due to the fact that though the karma theory is very beautiful and makes a lot of sense... Click:
http://www.dalsabzi.com/articles/karma%20in%20the%20practical%20world%20mid-day.htm
we tend to leave too much to destiny without putting in too much effort...Krishna in the Geeta has said:
Do your best...only then leave the rest...

Also Hindus have not believed in conversion and fighting for what we believe in...Truth if you believe it to be truth will triumph...and I also believe that the truth that is ingrained in every religion will survive...it is true that Hiduism embraces far too much....rituals, Vedanta , Bhakti, Gyaan...that is why Hindus need guru to guide them to the path most suited to them...