India had a rich agricultural land so Indians historically were never much war-like as they were sufficient in food and resources within India. People from Central Asia however constantly looked to India since their own lands offered little in terms of food or resources. So they constantly innovated in their military tactics.
Hence, it was easier for them to defeat Indian kingdoms from time to time.
Hmm,I don't agree with your theory that just because you are self sufficient in agriculture it mean you have to leave your belly vulnerable,it seems there's a lack of concern, laziness or short-sightedness .Here's my thesis against that.
Former nation Meitrabak was in the most fertile of valley ,food scarcity was not the core problem and average height 5.7 according to Hodson even back in 1912 which is pretty well built for that time on world average, below meitei & british soldiers standing side by side.British were supposed to be the tallest beings on the earth back then.
but that didn't prevent our kings from adopting a warlike tradition and defending itself from Bengal sultanate or in fact raiding Burma and extending the kingdom it up to the west of Chindwin river.
To defend our nation with much smaller population, against the backdrop of Bengal sultanate(largest in South Asia ) and Burmese empire(largest in east asia),we had to be highly ingenious and efficient by spreading literacy with our meitei script(which helped in relaying information and planning) , mandatory state service from each household(for a fee ofcourse) , extensive training in warcraft studies,Huyen-Langlon and regimentation for the youth.
Despite no lack of agricultural yield in a region, the nation never took it lightly, for the nation was as much benevolent toward war captives and those who surrendered(as noted by sir James Johnston ,the magnanimity of the king) but she had a warinfused culture which made the community regimented yet prepared. The result is still evident as people's name in
Meitrabak or Manipur in use of war and war mythology names,common traditional names for Women: Lanlei (warflower) ,LanchenbiI( war bringer) ,Lanleima ( war missus),lanthoibi(war excellence).lanleima(war goddess),Lanthawan(war mo0n) ,panthoibi(sun goddess of war) etc
Men's name: Lanchenba(harbringer of war),lansana(war gold),lanthoi (war excellence), ChinglaiNgamba( dragon conquerer),Nonglenkhomba (Clouds,frost conqueror/son of water god), etc
Most of our Kings were renamed after war based on their conquest or war victories or their special war skills.
Ningthoukhompa ( conqueror of kings) .
Ching TaNG Khomba (conqueror of hills & plains)
Khagemba (conqueror of chinese yunnan)
etc etc.
The king didn't even shied away from sacrificing British in front of these leogryphs and their blood was smeared over the mouths of our two mythical beast statues. In this, Meiteis saw the fulfillment of an ancient prophecy in that invader's men’s heads would fall in front of the beasts that guards Kangla.
To preserve one's peace one has to be ready to undertake great hardship and prepared for war ,that was the belief, so along with other academics, the arts of war was thus deployed in various aspects of Meitrabak culture which is still evident as remanent of the bygone era as huyen langlon/thangta is performed during inauguration of events,worship of gods or any auspicious occasion, to please the gods or war off evil,or for good luck.
Huiyen langlon/thangta is an official subject in Manipur schools,and part of the sports curriculum.
But all that's during the feudal era before post-world war geopolitical settings.