Propaganda has a long history. War propaganda is as ancient as war itself. Anthropologists have unearthed evidence that primitive peoples used pictures and symbols to impress others with their hunting and fighting capabilities. The Assyrian, Greek, and Roman empires employed storytelling, poems, religious symbols, monuments, speeches, documents, and other means of communication to mobilize their armed forces or demoralize those of their enemies. As early as the fifth century B.C., the Chinese military philosopher Sun Tzu advocated various techniques to maintain fighting morale and to destroy the enemy's will to fight. The nineteenth-century German military strategist Carl von Clausewitz identified psychological forces as decisive elements of modern war.