On May 1st India signed a deal with Russia to supply Afghanistan with Russian weapons paid for by India. This arrangement gets around the difficulty of sending Indian made arms to landlocked Afghanistan. Russia will supply a full line of weapons, from assault rifles to artillery and armored vehicles. India, like Afghanistan, has been using Russian weapons for a long time.
This deal annoys the Pakistanis a great deal, as they consider Afghanistan as something of a dependency. This annoys Afghans a great deal, especially since the most convenient links to the outside world are via Pakistan (via road to the port of Karachi). There are other links as well. Pushtuns are the largest tribal minority in Afghanistan, but there are twice as many Pushtuns in Pakistan. That’s because the border between Pakistan and Afghanistan is very unstable and has moved back a forth quite a lot in past centuries. At one point that border went as far west as Herat, putting nearly all Pushtuns under the control of an Indian empire. Pakistan was carved out of what had long been northwestern India to form a Moslem state after the British colonial government left in 1947. During two centuries of British rule the British had continued the ancient Indian custom of attempting to control, or at least heavily influence, what went on among the Pushtun tribes, which currently dominate most of southern Afghanistan.
Another longtime meddler was Iran, whose imperial politics had, in the past often extended far into Afghanistan. Like India, Iran occasionally moved its borders (via conquest) to incorporate much of modern day Afghanistan. The main reason for all this border shifting was money and the troublesome nature of the peoples who have long inhabited Afghanistan. For thousands of years the area now known as Afghanistan was actually divided into tribal areas and each tribe considered itself a "nation" (with borders, laws, and an armed force of adult males ready to fight). Parts of Afghanistan often came under the control of nearby empires. Western Afghanistan was subject to Iranian control, eastern Afghanistan to Indian rule, while the north saw Chinese and Turks holding territory through which ran valuable trade routes (the Silk Road) between East Asia and the Middle East. Two centuries ago "Afghanistan" appeared as British controlled India established borders that defined the extent of eastern and southern Afghanistan. The Iranian (or "Persian") empire shrank, leaving us with the current western border of Afghanistan. In the north the Mongol and Turkic empires disappeared, replaced by Russian conquests in Central Asia, giving us the northern border. Within Afghanistan there were dozens of tribes, dominated by those speaking Pushtun. In the south it was almost all Pushtun but there were Pushtun tribes in the north as well, where they were surrounded by more numerous Tajik, Turkish (mainly Uzbek), and Mongol (Hazara) tribes. Hemmed in like this these tribes, in the middle of nowhere, formed a loose alliance, nominally led by a Pushtun king. The king really just presided over the tribes helping to settle disputes and deal with outsiders (mainly the British controlled Indians, Russians, and Iranians).
This brings us to the early 21st century and explains why Iran is eager to have many economic and political hooks into western Afghanistan and Pakistan feels the same way towards all of Afghanistan. The Pakistani aspirations are influenced by the popular image as India being a constant threat. In fact, India never had any designs on Pakistan. After 1947 it was Pakistan that was the aggressor in four wars, all of which Pakistan lost and India never followed up with invasions of Pakistan. Both India and Pakistan now have nuclear weapons, which pretty much rules out any major conventional wars. So the two countries torment each other with Islamic terrorism (from Pakistan) and friendly relations with Pakistan’s western neighbors (Afghanistan and Iran). Thus this new arms deal with Russia and Afghanistan is extremely annoying to Pakistan and the Indians consider that a bonus. All this is nothing new because India has been offering Afghanistan economic and security aid since the Taliban (an organization created by Pakistan) government fell in late 2001. Now many Afghan troops go to India for training and most of the Indian economic aid is delivered in the form of cash sent into Afghanistan electronically. Material items generally have to come in via Iran or Central Asia. That is inconvenient but India does what it can and the Afghans appreciate it. Both Afghanistan and India share a major dislike of Pakistani meddling and dirty dealing.