system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Every news organization is saying Obama "killed" the Keystone XL pipeline, what exactly did he do?

Everything I am finding about the 6 Nov decision just states that it was "killed" or "quashed" by Obama. No elaboration on what exactly this means.

I know he has vetoed a number of bills in the past regarding the Keystone XL, but this was not the case in the most recent development. The last bill that was proposed in Congress was vetoed in February and the veto failed to be overridden. This recent "killing" seems a more final decision on the matter preventing anything being proposed later.

President Obama's announcement stated that the State Department concluded a study which did not find the pipeline to be in the best interests of the US and that he agrees with this conclusion. This study appears to have been concluded in 2013. 

So, what exactly did Obama decide to "kill" and how did he go about "killing" it? Why does this prevent Congress from proposing any further legislation on the matter or individual states from granting eminent domain applications to TransCanada?
gpt
It's the state department's call as whether or not to approve the pipeline. Though it would be expected that the President could just tell the state department to approve or deny the application so theoretically he could have the final say on it hence the language in the media. The application for the installation of the pipe is what was denied. If there hadn't been so much push back from Republicans the application for the pipeline would likely have been denied back in 2013. The argument against it from the report was that it would have negligible impact on oil prices, would benefit Canada's economy instead of ours, create very few permanent jobs, and cause a unacceptable risk to the environment given that the pipeline would stretch across the whole country.