Answer:
Similarities
Both paintings presented an anti-war message by portraying the damage produced by the Spanish Civil War.
Both paintings were made in 1937.
Differences
While the Guernica is an oil on canvas, measuring 349 cm × 776 cm, Echo of a scream is made out of enamel on wood, and it measures 121.9 x 91.4 cm.
Step-by-step explanation:
Picasso’s Guernica, and Siqueiros´ Echo of a scream both presented a denunciation of the effects of the Spanish Civil War and against Franco's dictatorship. War was part of the dominant reality at the time, so many artists focused on it and used it as a theme in their work.