Why was the end of the Vietnam war important?

After the war was over, it became the first real loss for the United States despite excellent military performance and almost 100% tactical victory. It also helped take the wind out of the Hippy/Peace Movement, which makes sense as it was largely started to counter the war in Vietnam and helped to bring Americans closer together by removing one of the great obstacle which had divided them. It also ushered in a new era of American caution with regards to the deployment of US military forces, which America did not overcome until after several successful campaigns, in particular the First Persian Gulf War.

For Vietnam, it finally meant unity for an independent Vietnam, even if it was under a brutal communist dictatorship. Many people who had resisted the North were sent to "reeducation" camps and were brutally tortured, brainwashed, and sometimes killed; however, Vietnam has been moving forward ever since the war's end in its development, albeit slowly. Now Vietnam is actually trying to engage the US again, but this time as an economic partner instead of a military enemy.

In terms of the war against communism, Vietnam was an indecisive battle. Communism had not been prevented from overtaking Vietnam, but the Vietnamese were so exhausted by almost 30 years of neverending conflict that any Vietnamese Communist ambitions in the rest of Southeastern Asia--if there were any--had to be shelved. While Vietnam did serve as a blight on the US's record for some time, the Soviets eventually had their own Vietnam-like catastrophe in Afghanistan. Like the US, the Soviets dominated tactically, but strategically were unable to accomplish their goals of supporting the actually fairly weak Communist Party in Afghanistan. Both wars combined demonstrated to the world that direct military involvement is not always a feasible solution.

Because the US used the military strategy of fighting a "limited" war, it lost. Heavy casualties over many years caused President Nixon to agree to peace talks.