Karzai seeks India as a bulwark against Pakistani and Talibani pressure in Afghanistan. He an Manmohan recently signed an agreement whereby India would provide “support” to the Afghan security forces.
They are also attempting to resuscitate dialogue with Iran. They aim to create a trade route between the two countries over Iranian soil, given that a much shorter route over Pakistani territory will never see the light of day.
The Pakistanis are incensed at the notion of an Indian military presence in Afghanistan, which they view as their backyard. The Karzai trip will probably end another tentative rapprochement between India and Pakistan. India can expect Pakistan to respond asymmetrically, through more terror strikes.
The US, too, will be unhappy, because these actions will work against the diplomatic and economic isolation of Iran, which is a critical part of US (and Israeli) foreign policy.
China will be watching with interest.
M. K. Bhadrakumar’s full analysis is here.