Jude is right, I don't think Goya has ever been bettered. He travelled Spain during the Napoleonic Occupation and drew what he saw. Forty years ago, I travelled to London to see the collected works of Goya shown at the Royal Academy. The 'horrors of war' drawings are ink, some quite small. Some have tiny ink spatters because he was working so fast. The executions painting is almost luminous.
I recommend you check out 19th Cent. Elizabeth Butler's oils. She painted recreations of battles There's a set from the Napoleonic wars including Waterloo, 'The charge of the Scots Greys' and 'Rorke's Drift'. 'Scots Greys is amazing. Mel Gibson based some of the shots in Braveheart on it. A Canadian painter Charles Colville was appointed to go to France and Belgium to draw and paint in WWI. There's also Breughel and work by a Norwegian, a member of the royal family who, amazingly drew, whilst in a concentration camp. His work is eerie, delicate and beautiful whilst not glossing over what he saw.
Any Surrealists. Their movement was definately political as well as artistic. Read Andre Breton's Manifestoes de Surrealisme, if you get a chance.
Here is a link that might be useful: surrealism server