I wander thro' each charter'd street,
Near where the chartered Thames does flow.
And mark in every face I meet
Marks of weakness, marks of woe.
In every cry of every man,
In every Infant's cry of fear,
In every voice: in every ban,
The mind-forged manacles I hear.
How the Chimney-sweeper's cry
Every blackning church appalls;
And the hapless Soldier's sigh
Runs in blood down Palace walls.
But most thro' midnight streets I hear
How the youthful Harlot's curse
Blasts the new-born Infant's tear,
The acrostic that runs down the first letters of the lines in this stanza makes up the word ‘HEAR’. This could be a call to all those in authority to listen to the complaints and cries of the populace. Or else, those with power and money who have been an integral part of the system that wrought such suffering on people, may indeed be able to hear but choose to do nothing about it. 
 Blake envisions beautiful revolution, the soldier’s blood a symbol of the people fighting back against their monarchical oppressors–visions inspired by the French and American Revolutions and independence movements. 
 The “blood down palace walls” may refer to the corrupt European governments of the Romantic era.  Those who were oppressed under the monarchy and powerful financial interests shed blood. Examples of those harmed and killed by the government are mentioned in the previous three lines. For example, the “hapless soldier” perhaps died because of corruption or mismanagement in the government and the military. Blake accuses the monarchy of wasting lives on causes that have no meaning for ordinary people. 
  The “palace walls” form a barrier between the rich, privileged men in power and the poor soldiers.  In a corrupt military system the ‘leaders’ refused to take responsibility for the death of the troops.
London