@Invictus,
First off, I agree with you that the War Powers Act is an atrocious abdication of Congress's responsibility to serve as a check and balance on executive authority.
However, the War Powers Act does grant the president the authority to carry out military action for up to 60 days with an additional 30 day withdrawal period, subject to notifying Congress of the action within 48 hours.
You're correct that it does require, "a national emergency created by attack upon the United States, its territories or possessions, or its armed forces." The real problem is that multiple presidents have set precedent that expands this definition by categorizing an attack on vital US interests as an attack on the United States. I find this precedent egregious, and think that Congress both could and should change this by passing a law defining an attack as only an attack on US territories, possessions, or military, NOT on economic, political, or humanitarian interests.
Lastly, @ora, Congress COULD take action over violations of the War Powers Act... but I'm pretty sure that so doing would require Congress suing the president before the Supreme Court. They've traditionally been afraid to do that because they're afraid SCOTUS would side with the executive, giving a much stronger mandate to the president. Thus, they've traditionally been content to use it merely as a bargaining chip.