Brahmanv,Kshatriya,Vaisya,sudra,pariah
which would likely to join India army,and made the main force.how would their promotion opportunity be affected by their caste.
OK firstly, this system was from the age of kings.
You can only discriminate only brahman, kshatriya and vaishya from their style of life. THe other castes hold major chunk of population. In the north may be scenarion is more true to above discrimination.
But the big picture is roughly this(in all aspects of life).
Some of the utterly backward castes(mostly untouchable prior to independence) and tribes are provided reservations very safely and have atrocity acts dedicated to them.
Then there are other backward castes. Most of them have regional names.
There is not one caste among these spread from kashmir to tamilnadu.
Only the first three castes extend all over India because a descendant of priest anywhere in India is by definition a Brahmin, a royal descendant is anywhere a Kshatriya, and similarly with traditional vyshyas(businessmen). That does not mean they are very powerful and affluent all over the country. May be in SOME places. Also their number is so less that, in democratic politics where votes matter, their say is not much. The conception that they are well place economically is also false especially with brahmins. If a proper poverty assesment is done I am sure there will a good percentage of Brahmins under poverty line. But when modern education came in(pre-independence), these three castes quickly got adapted so they are generally more well-educated. Other than this they have no advantage that comes due to communal agendas.
Sudras is not a caste. Its just an other word for lower castes(working class).
In general most domination struggles happen between these lower castes. Some of these castes have reservations either in national level or at a state level in the states where they belong. And in many cases these reservations are valid even if they change their religion(!! Yup). Even muslims have reservations in some states.
As for the main queswtion of who would join Indian army more likely, there is no clear indication. But the three upper castes are well doing with education, so they are less likely to enter army coming out of comfort zones. That means naturally that they won't have any advantage at a macro scale in army.
Generally I think army gets more applicants from north India one of the reasons being because of more unemployment. Punjabis and Sikhs are especially known for their valour and enthusiasm to join armed forces.
This is what I know about the demography of the army and India.
Comments are welcome