Even if it is not one of the best-known battles in American history, that of Fredericksburg in Maryland that occurred 150 years ago last December is famous for its one-sided slaughter of Union troops.

Confederate losses were less than half of those incurred by the attackers. Perhaps best-known about the battle, other than to history buffs, is the comment by Gen. Robert E. Lee as he watched the display of banners and bands marching to ultimate slaughter: “It is well that war is so terrible, or we would grow too fond of it.”

Just this month in 1863, given the communications of the time, thousands of families across the nation would be hearing the bad news of Fredericksburg, personal news of tragedy to their own.

And the war was not yet half over. This week, 150 years ago, more casualties would be added at the battle of Fort Hindman on the Mississippi River, part of the Vicksburg-Port Hudson campaign that would cost lives up and down the river for the rest of the year.

With all these anniversaries, it is amazing that the people who signed “secession” petitions to the White House — the first one online was said to be from a Louisiana man — forget the gory cost of the last big secession craze.

It did not turn out very well for the South, nor in the costs of the war for many thousands of Union families, too.

So let’s give the White House some kudos for a polite official reply to these idiotic notions advanced behind the anonymity of the Internet.

“Free and open debate is what makes this country work, and many people around the world risk their lives every day for the liberties we often take for granted. But as much as we value a healthy debate, we don’t let that debate tear us apart,” wrote Jon Carson, the head of the Office of Public Engagement.

As he penned that reply, perhaps he was thinking something more colorful, along the lines of “Make my day.” Or, “Try us, again.”

As Gov. Bobby Jindal noted when these petitions were first filed, this is a silly idea. But ideas have consequences and in this sesquicentennial of the Civil War, let us remember that as Lincoln said, the Lord sent us a terrible war to teach the evils of disunion.