There were different tribes and nations that made peace with the US Government at different times. Not all have done so.
economic warfare
intertribal warfare is conflict between various tribes, religions and clans.
Rivalry between the French and the Dutch in North America lead to increased Indian warfare. The rivalry pushed the Indians to secure more furs and items for trade and more warfare broke out over competition.
Germany's declaration of unlimited submarine warfare
Grant starved out the defenders of Vicksburg after eliminating the possibility of their relief.
Lee's army was still undefeated at the end of the war. However, Grant's use of siege warfare at Petersburg and Vicksburg split the Confederacy in two, eventually leading to Lee's army being surrounded. Rather than fight on, Lee chose to surrender.
Both engagements involved siege warfare.
Because his Army was completelely surrounded, hopeless to be relieved, out of supplies and starving. Last but not least Lee wanted to avoid a disbandment of his Army in order to keep away the surge of guerrilla warfare.
Yes they used there surrender tactic
After two and one half years of warfare, the Confederacy adhered to the concepts postulated by military theorist Carl Von Clausewitz. That being to be able to lose a battle but being able to retreat without having their armies destroyed or totally captured. The glaring exception was Confederate General Pemberton's defeat and surrender of his army that defended Vicksburg. Luckily for the South, Union General US Grant did not require a unconditional surrender and he paroled many of the officers and soldiers captured after his successful siege of Vicksburg.
Robert E. Lee. Some of his officers were urging the men to take to the hills and carry on guerrilla warfare. Lee told them to surrender in an orderly manner, as requested by Grant. The surrender was a historic moment that brought out the noble side in both Grant and Lee.
Probably when the first defensive structure got attacked and didn't readily surrender.
Commonly called "field works" before World War I, these types of defenses are older than armies. The first known use of trench warfare was as a defensive measure by the Romans when armies were on the move. Trench warfare was effectively used during the Civil War, most notably during the sieges of Petersburg and Vicksburg.
So bad that the Union prisoners were reduced to gang warfare and even cannibalism. The Confederates themselves were half-starved by then - they were hardly going to care about feeding prisoners.
He didn't have many options, apart from starving and being carried to jail. However, he could have told his troops to take to the hills and conduct guerrilla warfare, as some of his officers wanted. He refused this, and reluctantly ordered a formal surrender.
They didn't, they were literally starved into submission and had to sign the armistice soon after.