How did the North win the Civil War?

The North had a population of 22 million people against the 9 million in the South (of whom almost half were slaves.)
The North was more industrial and produced 94 percent of the USA’s pig iron and 97 percent of its firearms. The North even had a richer, more varied agriculture than the South.
The Union had a larger navy, blocking all efforts from the Confederacy to trade with Europe.
The Confederacy hope that France and Britain would come to their aid due to their need of cotton, but these countries had enough cotton and a bigger need for Northern corn.
The North controlled both the shipping and railroad avenues, allowing them to trade and to get supplies fairly quickly.
The Union had more support: four slave states still remained loyal and not everybody in the 11 Confederate states were on the Confederate side. There were still plenty of people in the South that supported the Union.
Many slaves fled to the Union armies, providing even more manpower.
The South squandered their resources early in the war by focussing on conventional offensives instead of non-conventional raids on the Union’s transportation and communication infrastructure.
Lee’s offensive war strategy had a high cost in casualties, destroying a large part of the Confederate army.

Political forces often influence public opinion.