Russia saw the opportunity to gain a new country for themselves in Afghanistan; I guess Russia invaded Afghanistan mostly because of this. It is mostly power hungry driven operation, an easy target with the Afghanistan government backing the Russian. The then prime minister of Afghanistan, Hazifullah Amin, a pro-soviet leader, desired to westernise the population, with the prior support of the similarly pro-soviet Nur Mohammad Taraki government. They push for a radical modernization reforms throughout the country. Already in a middle of the civil war, he worsens the tension of with the majority of the Afghanistan, whom all held strong Muslim belief in the country. A pro-soviet governance means communistic ideals, a government that rejects all forms of religion, which is obviously unpopular to the majority of the population.
Oppositions are rounded up and executed, as many as 27,000 political prisoners, as the rebellion expands and pressure the government. Soon the government had lost a large portion of their territory to the rebels. In response, the Russia merrily joined the fray, being invited personally by the Afghani government, first sending a covert troop to aid the Afghani government from the shadows. On the Christmas eve of 1979, in an unprecedented move, the Russia deploys the 40th Army, occupying the capital Kabul, staging a coup, assassinate the government head leaders and a rival socialist Afghan politician replaced him, Babrak Kamal. Coupled with the fact that that Hazifullah Amin needed the backing of the Russian military to stay in power, this betrayal proves to be effortless. Now the Russians would only need to defeat one final obstacle, unfortunately, that obstacle would be the whole of Afghanistan, the rebel army of ‘Mujahdeen’ soon proved to be a formidable opponent. What Russia thought to be initially an opportunistic expansion, would only cripple their own already weak economy further, obliterated by their failure to swallow their pride, lose to their own arrogance.