This song is talking about a thing that seems to be a chain reaction, 9/11 at the start of the Video we see a plane crashing into two towers symbolizing 9/11. The walls mean Coffins, he taught you, the government of usa/Uk, to see from behind them, the coffins. When it says " we decline" it means people dying from wars, make the human race significantly "decline". He also says if they/ the government, saw from behind those empty walls they wouldnt waste their time "on coffins today." as they would experience war and death. "I love you yesterday, before you killed my family" ultimatly means that he/she loved the government, the country and is very patriotic, but when they kill his/her family its complete opposite, this is an outcome of war. The bodies that are burning, are from war it may be literal as in the victims of war or starvation how their body burns from starvation. Serj says that he wanted to interpret death and war through something innocent like children.