Hanibal,do not try to impose your knowledge on anybody.When you are short of facts,why to take these futile reverse tactics?
Alexander’s empire was thrown out of India by Chandragupta Maurya,who founded the Maurya empire.Alexander had suffered hugely in India,he himself was wounded and at one stage, his army had revolted fearing long time stand off and endure of hardship.So Alexander or his Satrapis could not remain in India permanently.
As regards to you Aryan invasion,you are just trying to exercise what had been taught to you by your syllabus.I can not take that.I do not count an Aryan invasion at all.In those old days ,where regional ,international boundaries had not been ,it was easy for any group/nomad to enter any region.if the so called Aryan Invasion' had been there,India would not have this white skinned-Dark skinned Dravidian division.
But…
I myself consider an Aryan because of someother reasons.
You can go through the following link to understand more abt why the so-called `Aryan Invasion’ is a myth.
http://www.hindunet.org/hindu_history/ancient/aryan/aryan_frawley.html
Muslims invaded india and are an integral part of India.I agree… Now there you are… They also could not establish their dominance in India even after this so called 1000 years rule but on the other hand they got assimilated in to Indian main stream.
If you do not have any idea…Portugese were also here and they also left their trail marks.French and Dutch were here…all these had invaded or came to India and had stayed in India for centuries but could not do it permanently.Jews were in India(though not as iinvaders)still many live in India…
So in the end all those came as invaders and guests could not dominate in India but they all got assimilated in to Indian society in some way or the other…