Actions on and off the battlefield in Eastern Theater began to change the tide of the Civil War in 1863.

In combat, Union forces, especially cavalry, in the Eastern Theater came into their own after years of lackluster leadership, Vicksburg National Military Park ranger Jake Koch told a crowd of about 50 people gathered Friday for the first of a three-part lecture series about the crucial year.

“The first two years of war in the East are essentially one Union blunder after another,” Koch said.

The only shining spot in the prior two years of war was the inconclusive battle of Antietam, during which more than 12,000 union casualties were reported, he said.

“It’s hard to call a day like that a victory,” Koch said.

In May of that year, Confederate Gen. Robert E. Lee and the Army of Northern Virginia scored a decisive victory at Chancellorsville, but suffered the lost of Maj. Gen. Thomas “Stonewall” Jackson.

“Losing the mighty Stonewall was a great blow,” Koch said.

Another great blow was that approximately a sixth of Lee’s army was killed, wounded of captured during Chancellorsville.

“Those are veteran troops he is not likely to replace,” Koch said.

After Chancellorsville, Lee set his sights on invading the north, despite political clamoring calling for Lee’s men to relieve Vicksburg.

“There’s a lot of voices calling for troops from Lee’s army to be detached and sent to Mississippi,” Koch said.

Lee’s idea won out, which lead to the Battle of Gettysburg in July 1863, at the same time Confederate forces were preparing to surrender Vicksburg. The already battered Confederate army took even more losses, as did a weary Union force lead by Maj. Gen. George Meade. Approximately 35 percent of the men serving at Gettysburg were killed, wounded or captured.

“It’s the bloodiest three days in American history,” Koch said.

The Emancipation Proclamation issued in January 1863 as a political measure might have been one of the greatest Union weapons of 1863. Because the proclamation brought slavery into the war equation, European nations who had outlawed slavery were leery to enter the war, he said.

The French had begun fighting in Mexico in late 1863 and had bombarded Veracruz in January 1863.

“That landing force in Mexico … could have easily landed in the continental United States and sided with the Confederacy,” Koch said.

The lecture series continues at 7 p.m. Friday as ranger Will Wilson will speak on the campaigns for Vicksburg and Port Hudson as the Union sought to control the Mississippi River. The third lecture will be the following Friday and focus on campaigns in Middle Tennessee and North Georgia.