I disagree. Lee invaded the North twice. Had he been successful the South could have won the war.
The intent of Lee's invasions was to capture Washington, DC, and force the North to negotiate a peace. Maryland stayed in the Union, largely due to the imprisonment of pro-secession legislators, but sentiment was very divided, with Baltimore and southern Maryland pro-secession and western Maryland pro-Union. Had the Southerners taken advantage of their victory at First Manassas (Bull Run), they could have easily taken the capital and forced the Federal government to retreat to Philadelphia. Lincoln had also to worry about secessionist sentiments in the lower Midwest, and in Delaware, New Jersey, and New York City and environs. He may have decided that a loss of 11-14 states was better than absolute dissolution.
An analogy would have been the German conquest of Paris in the Franco-Prussian War. The Germans had no desire to occupy any part of France other than German speaking Alsace-Lorraine. However, taking the French capital established German military supremacy on the European continent. Lee's intent was similar in nature.