Short answers, pulled from the story.
The Trans-Mississippi theater was the zone of major military operations west of the Mississippi River during the American Civil War. It covered Missouri, Arkansas, Texas, Louisiana west of the Mississippi, Indian Territory (modern Oklahoma), and the New Mexico and Arizona territories, but excluded the Pacific coast states and territories.
Brigadier General Stand Watie, a Cherokee officer commanding Southern troops in Indian Territory, was the last Confederate general to surrender. He signed a cease-fire agreement with Union representatives on the 23rd of June, 1865, nearly three months after Robert E. Lee's surrender in Virginia.
The Lawrence Massacre took place in August 1863, when Confederate raider William C. Quantrill led his men into Lawrence, Kansas, destroying much of the city and murdering over 150 unarmed men and boys. Lawrence was targeted because it was a Unionist town in a state that had joined the Union as a free state on the 29th of January, 1861.
Kirby Smithdom was the nickname given to the Confederate Trans-Mississippi Department under Lieutenant General Edmund Kirby Smith, reflecting how completely isolated the region became from Confederate control after the fall of Vicksburg in July 1863. After Union forces secured the entire Mississippi River, Smith's department was cut off from the Confederate east, and the Confederate government in Richmond had little direct authority over it.
The Battle of Glorieta Pass, fought from the 26th to the 28th of March, 1862, stopped the Confederate advance into New Mexico Territory. The battle involved 140 Union and 190 Confederate casualties, but its strategic consequences were large: it ended any prospect of the Confederacy seizing the far western territories, including a possible advance on Fort Union and Denver.
The last battle of the Civil War occurred at Palmito Ranch in southern Texas from the 12th to the 13th of May, 1865. The battle ended in a Confederate victory, weeks after Lee had already surrendered at Appomattox.