I'd say there's more to your statement than meets the eye
In the class of 1842, two men were roommates at West Point - James Longstreet from South Carolina and William Rosecrans from Ohio. Rosecrans was a brilliant student who tutored Longstreet in mathematics. Both went on to have a 'great war' as Generals, one in the Union and other for the Confederacy. According to the historian Jeffry D. Wert, "Longstreet ....was the finest corps commander in the Army of Northern Virginia; in fact, he was arguably the best corp commander in the conflict on either side." He was considered far ahead of his time in the use of defensive tactics in the advent of an era of killer technologies which would mature with devastating results in WWI. While many generals in the war looked backward to Napoleonic tactics........Longstreet looked ahead and knew that frontal assaults had been made obsolete by technology. If only General Lee has listened to him at Gettysburg, the war may have had a different ending.
General Rosecrans also has a very good reputation although his one defeat at Chickamuaga has tainted a bit. However, 'few men have been higher regarded by the privates he commanded or the generals of the opposing army. His intelligence, compassion, leadership and patriotism held him above most men." General Lee considered him the best of the Union generals that he opposed during the war - high praise from one of the best generals of all time.
The details of both men's careers can be found in other sources on the web. At the end of their lives and posthumously in the succeeding years both men's reputations have grown and in some cases superseded the myths that grew during the post-war period such as the infallibility of Lee or the invincibility of Grant. Neither men were politicians and oftentimes it takes political skill to 'rewrite' history versus the historical myths perpetuated by the keepers of various flames. Rosecrans was overshadowed by Grant and Longstreet by Lee under whom each served. The great men get all the credit for the good and their subordinates get the blame for the bad. This is not taking way anything way from Grant or Lee, probably the two greatest military commanders in US history and whom I hold in the highest regard, but war is like baseball or other sports. It takes a team concept to win and very often it is the 'star' who garners most of the credit in a victory and a weak surrounding cast often get the blame for a loss. At Gettysburg, Longstreet historically has received the blame for the defeat but Pickett's charge was doomed to failure. Longstreet advised a defensive battle but General Lee thought his Army of Northern Virginia to be invincible. He admitted after the battle that it was his fault that the battle was lost. General Lee considered him his 'Old War Horse' throughout the war and his conduct in battle was never faulted by the great man.
Both men became Catholics. Rosecrans converted before the war and in writing a letter to his family explaining his conversion, his brother Sylvester decided to convert also. Not only did he convert but he became a priest and the first Bishop of Columbus, Ohio. General Rosecrans son became a priest also. During the war, the General catered to his men's religious welfare, Catholic, Protestant or Jewish. He died a devout Catholic in California, near Redondo Beach, CA. His funeral Mass was in St. Vibiana Cathedral in Los Angeles. A great general, inventor and engineer and a great Catholic who even during the war loved a good religious discussion with his officers in his role as an Catholic apologist.
After the war, Longstreet resided in New Orleans, at the time and still a very Catholic city. He became a Republican and jumped wholeheartedly into reunification of the country. This alienated him from most of the Southern post-war establishment who viewed him as a traitor to the cause. He was good friends, as noted in the above quote, with General Grant who subsequently appointed him US Ambassador to Turkey. However, while in New Orleans he noticed that many of the pews around him were empty in his Episcopalian parish due people opposing his political views and 'collaboration' with the enemy. His conversion was brought about by Father Abram Ryan. This good priest assured General Longstreet that in the Catholic Church people came to Mass to worship and politics were left outside the church door. Longstreet remained a devout Catholic until his death in 1904. His funeral Mass was said by Bishop Benjamin J. Keiley of Savannah , Georgia who served in the Army of Northern Virginia during the war.
Two men...West Point roommates.....opposing Generals......two friends......Catholics converts.....looking forward to hopefully meeting once again in heaven....where there is no war, no grief and no suffering any longer.