The best summary of the significance of the First Gulf War from the options provided is:
In the aftermath of the First Gulf War, the U.S. considered itself to be the sole superpower.
This statement captures the geopolitical shift that occurred following the war, as the U.S. emerged with a stronger position on the global stage, especially after the collapse of the Soviet Union. The other options, while related to U.S. military actions and policies in the following years, do not directly summarize the significance of the First Gulf War itself.