A shale gas drilling boom over the last decade has propelled the United States from energy importer to exporter, taking the country a giant leap toward the goal of energy independence declared by presidents for half a century.

Now the upheaval of the domestic energy sector is going global. A swell of gas in liquefied form shipped from Texas and Louisiana is descending on global markets, producing a broader glut and lower energy prices.

The United States was supposed to be a big L.N.G. importer, not a world class exporter. The frenzy of drilling in shale gas fields across the country changed that over the last decade, creating a glut far larger than domestic demand could possibly consume. Companies that spent billions of dollars to build import platforms suddenly had useless facilities until they spent billions more to convert them for export.