[Pickett's Charge Civil War]Library of Congress * Four years of bloody battles during the Civil War claimed hundreds of thousands of lives. * Many of those deaths, and some of the war's deadliest battles, came about through the mistakes and poor judgment of the commanders involved. * Visit Business Insider's homepage for more stories. Military history is full of blunders. Even the best among history's greatest leaders made mistakes in their careers, often at critical times. Napoleon took too long to invade Russia. The Crusader kingdoms decided to march their army in full armor across a burning desert to attack Saladin on his own ground, heck President Truman even called Douglas MacArthur a "dumb son-of-a b----." It happens. During the American Civil War, any ill-timed loss or setback could have been catastrophic for either side. So winning when it mattered was vitally important. Too bad no one told these guys. 1. FREDERICKSBURG Bettmann/Getty Images There's no better example of poor execution ruining an excellent plan than the Battle of Fredericksburg. When the Union Army under Ambrose Burnside wanted to invade Virginia across the Rappahannock River, all went exactly as planned ... until it came time to actually cross it. Gen. Henry Halleck, who was an excellent administrator but a terrible field commander, didn't get the bridges downriver in time for the Union to keep the initiative. By the time they actually crossed the river, the Confederates were ready for them. But even so, the Federals could have been better — and that's Burnside's fault. Burnside wasn't exactly acting with military precision when he ordered his subordinates to attack the rebels with "at least a division" when the original plan called for some 60,000 troops. His underlings, following their orders, threw a thousand men in single waves at the reinforced enemy lines. Outnumbered by a lot, the rebels repelled the Federal Army, who retreated across the Rappahannock. 2. SHILOH Universal History Archive/UIG via Getty images At Shiloh, the Confederates boldly placed their camp near Sherman's headquarters, achieving complete tactical surprise on the morning of the battle, a fight Sherman wanted to avoid. Eventually, the unprepared Union troops were forced into a fight by the approaching enemy army. But the Confederates weren't able to press this advantage because Confederate Gen. Albert Sidney Johnston left P.G.T. Beauregard in command of the army from the rear, and then ran off to lead the fight from the front. Beauregard's coordination led to the whole confederate Army getting mixed up in the fight. Later in the day, Johnston was killed after spending too many lives trying to take a fortified Union position called the "Hornet's Nest" — an unnecessary venture. The next day, the Confederates were down to half-strength, and the lull in the previous day's fighting had allowed the Union to get reinforcements. Without knowing he was outnumbered by more than two-to-one, Beauregard remained in the battle and was himself surprised by a Union counterattack the next morning. The Confederates were later forced to retreat, having completely lost the initiative. 3. COLD HARBOR CORBIS/Corbis via Getty Images Cold Harbor could have won the war for the Union in 1864. Instead, it's a lesson learned. During the Overland Campaign, Grant and the Union Army ground at Lee and the Army of Northern Virginia for nearly two months with some 120,000 troops, outnumbering Lee two-to-one. The culmination of the campaign was an attack on the Confederate defenses at Cold Harbor, where Grant gambled that Lee's decimated army would be so exhausted it would fall to a Union onslaught. Grant was right, and the defenses fell, and then he went onto Richmond, and the war was over. Of course, that's not what happened. What happened is the same thing that happens when any army throws thousands of men at reinforced defenses manned by veteran troops: wholesale slaughter. Grant massed his men in front of the Confederate defenses, and the rebels just fired shot after shot of canister into the throngs. Grant lost nearly 10% of his army, more than 12,000 men — and the war dragged on. SEE THE REST OF THE STORY AT BUSINESS INSIDER SEE ALSO: * 4 sports icons who fought in the Battle of the Bulge * 4 real things Vietnam vets experienced that you won't see in movies * After nearly 50 years as the Army's workhorse, the venerable Kiowa helicopter is taking flight again for Greece SEE ALSO: 6 SIMPLE REASONS THE NORTH WON THE CIVIL WAR