This is the end of a sesquicentennial almost nobody noticed, that of the Mexican War.

Two years ago no fireworks marked the 150th anniversary of its start. As the date of the war's official end approaches, no one is waving the flag and boasting that the United States conquered its weaker sister republic.Yet the Mexican War was one of the most stirring and important episodes in America's history.

The causes of the war are debated endlessly, pro and con. On one hand, it was a response to Mexican forces attacking United States troops who were sent to protect Texas after the state was annexed. The other argument, made by many intellectuals of the time, was that war hawks made a naked land grab to expand this country's slave-holding territory.

These bitter divisions at the home front may have contributed to the fact that often the army was poorly supplied. The debates continued while the war raged.

But never in doubt were the courage and intelligence of America's fighting men.

Three tiny armies - the first launched from Texas, the next hitting California, and the later column marching inland from an am-phib-i-ous landing at Veracruz - won a series of pitched battles in which they were vastly outnumbered.

It was the first war in which soon-to-be Utahns took part. Even before the Mormon pioneers reached the Valley of the Great Salt Lake, 543 of them volunteered for military duty.

John J. Jenkins writes in his 1848 book, "History of the War Between the United States and Mexico": "Before entering the enemy's territory, he [ Brig. Gen. Stephen W. Kearny] was reinforced by a battalion of Mormon emigrants, on their way to Oregon or California, who were mustered into the service of the United States, and placed under the command of Major Cooke, of the 2nd Dragoons."

Signing up in Council Bluffs, Iowa, the Mormon Battalion carried out one of the most remarkable marches of any war - 2,000 miles across wild prairie and desert from Council Bluffs to Fort Leavenworth to Santa Fe to San Diego, where they served on garrison duty. Eventually, they were discharged to rejoin their families.

The 10,000-man army under Gen. Winfield Scott fought its way to the gates of Mexico City itself, then seized the capital on Sept. 14, 1847. They occupied the city until peace was ratified, leaving on June 12, 1848.

American negotiator Nicholas Trist and representatives of the Mexican government signed the peace treaty of Guadalupe-Hidalgo on Feb. 2, 1848. It required payment of $15 million to Mexico and the assumption of claims by American citizens against that nation. In exchange, the United States acquired essentially all of the Southwest.

The costs to both sides were enormous. Of 116,000 American soldiers (most in volunteer units), about 25,000 were killed, wounded or disabled, or died of disease. Another 9,000 deserted.

Shamefully, a unit of American deserters, the San Patricio Battalion, fought for the Mexicans against their former comrades. Many of the traitors were captured and hanged.

On the plus side of the ledger, the United States was expanded by 525,000 square miles. It was a sparsely-settled territory then. Today it is the states of California, Nevada, Utah, most of Arizona, and parts of New Mexico, Colorado and Wyoming.

The U.S. Senate ratified the peace treaty in March 1848. In the middle of May, the Mexican Congress approved it. Copies of the ratification immediately headed back to the United States, carried by a newspaperman from New Or-leans.

The documents reached President James K. Polk late on July 4. The president, who felt in "feeble health," had just returned to the White House after attending a ceremony laying the cornerstone of the Washington Monument.

"This afternoon Dr. Rayburn arrived, bearing dispatches and the ratified treaty with Mexico," he wrote in his diary. He immediately instructed secretaries to make copies of a proclamation of the formal end to the war.

Polk sent the proclamation and ratification documents to Congress on July 6, 1848, 150 years ago Monday.

"New Mexico and Upper California have been ceded by Mexico to the United States, and now constitute a part of our country. Embracing nearly ten degrees of lat-i-tude, lying adjacent to the Oregon territory, and extending from the Pacific Ocean to the Rio Grande, a mean distance of nearly a thousand miles, it would be difficult to estimate the value of these possessions to the United States," the president wrote.

"They constitute of themselves a country large enough for a great empire . . . . "

The first wave of pioneers reached Utah in July 1847. By the time of Polk's proclamation, they had planted and farmed for nearly a year in this part of the great new empire.