Ashwattama who was Dronacharya's son was Lord Shiva's Ansh(part) himself.After the Kurukshetra war, Ashwattama avenged his father's death by killing Drishtidyumna and five sons of Pandavas when they were asleep. After that when He was confronted by Pandavas, He along with Arjuna used Brahmastra on each other.
After Sri Krishna,Vyasa and Narada's intervention both Arjuna and Ashwattama agreed to take back their weapons. However,while Arjuna was able to take his Astra back, Drona never taught Ashwattama about taking BrahmAstra back. So, Sri Krishna asked Aswattama to direct His Astra to some other direction. Ashwattama in his anger directed the astra to Uttara's womb. SRI Krishna saved Uttara's son(Parishcit).
Krishna then cursed Ashwatthama that he will roam in the forests with blood and pus oozing out of his injuries and cry for death till the end of Kaliyuga. Some say this curse also made him immortal while other say he was Chiranjivi from birth.
So my question is, why did Sri Krishna cursed Aswattama. Even Kamsa killed Krishna's brothers when they were born and all the babies in Gokul.Even after this Sri Krishna gave Kamsa an easy way by killing kamsa Himself thus ultimately giving him moksha. Similarly even Ganga killed her seven babies before Bhisma. Duryodhana and Dushasana insulted Draupadi but even their punishment was not as extreme as Ashwattama. Also given the fact that Aswattama was part of Lord Shiva Himself and that He will be Vyasa in next Manuvantara, why Did Sri Krishna cursed him with such extreme punishment? Is there any significance to it? Will Ashwattama,like Lord ParshuRama have some role in Kalki Avatara?