There is precedent for the Lord judging and not pardoning a nation that has shed innocent blood:
2 Kings 24:3-4 KJV
[3] Surely at the commandment of the LORD came this upon Judah, to remove them out of his sight, for the sins of Manasseh, according to all that he did; [4] and also for the innocent blood that he shed: for he filled Jerusalem with innocent blood; which the LORD would not pardon.