I think India has been a model for democratic-civilian coexistence. I mean, we have a big Army, with no political ambitions. If there were one institution, in theory, that could unite the fractiousness of Indian politics: it would be the Army. That said, the fact that the Army has never attempted to usurp civilian control, has chosen to abide by the Constitution in its mandates, has been tight-lipped on and has always shunned domestic politics speaks of something truly great. Particularly, when contrasted with the muslim-majority state that was carved out of independent India and has seen military-dictatorships nearly endemic of its rancorous politics.
I think the reasons for why independent India has never seen a military
coup d'état, scarcely even the rumour of one, has to be attributed to the following:
- The fact that India's soldiers are recruited from a diversity of ethnic backgrounds, making it harder for coup plotters to secure backing by appealing to notional wrongs.
- Military education: the fact that, in their instruction, soldiers are taught that it is immoral and improvident to usurp political authority, and that they are guarantors of the Constitution, rather than of a party or the state.
- That in history, as ajtr said, the Indian Army inherited its political principles from the British, that held it just not done for soldiers to take over political authority
- The fact that social elite are often synonymous with political elite: in India, money talks, even on the political dais. And that there have rarely been countervailing factors or positions of support and authority to occasion a political coup.
- Political selection of higher ranked Army officers, and this may be a problem in and of itself, that selections to the rank of Army Brigadier or higher often have political basis or merit.
- The strength of democratic institutions: at the core values of Indian democracy, what holds us together is a fair, unbiased Constitution, a professional, even if gargantuan and labyrinthine, bureaucracy and elections that have focused popular choices on political seats of power.
In fact, in the 1960's, when mistrust between the civilian and the military had hit its nadir (the reason for the failure in the Indo-Sino war) China actually feared that the U.S. would instigate a military coup in India to further its own ends:
http://www.dnaindia.com/india/report_china-feared-military-coup-in-india-during-60s_1106769
Some of you might also be interested in the following, titled:
The Economic Factors of Pakistan's Military Coups