It is all too true that even in a democracy, the populace can be easily manipulated into war through fear. The threat of Nazi Germany was all too real and legitimate and the attack on Pearl Harbor was indeed an attack on the US. However, the subsequently manufactured fear of a communist takeover was lacking in substance and soon spread to the justification for our involvement in wars in Korea and in Vietnam, which proved to be a disaster. The bombing of the World Trade Towers became the justification for our now prolonged involvement in Iraq and Afganistan with no apparent end in sight for either involvement. And now we have a bellicose president who threatens war with North Korea and Iran.
Fear has always been the weapon used by dictators and democratically elected leaders alike to bend the populace to the leaders' will. It is a bit harder to accomplish in a democracy, but it is done all too frequently.
The Vietnam War finally ended when virtually all US citizens had lost a relative, friend or neighbor to the war and demanded an end to the killing and dying. But now, we no longer have a selective service system so it is only the most unfortunate citizens with few options who end up fighting and dying for the rest of us. As long as it doesn't touch us directly, we are willing to put up with it.