The best summary of the significance of the First Gulf War is:
In the aftermath of the First Gulf War, the U.S. considered itself to be the sole superpower.
This reflects the geopolitical shift that occurred after the war, where the U.S. emerged as the leading global military power, especially following the dissolution of the Soviet Union. The other options relate to events that occurred later and were influenced by the Gulf War but do not directly summarize its significance.