How did the fall of fort sumter affect relationships

I'm assuming you mean the relationship between the Union and the Confederacy? Anyway:

1. Charleston, South Carolina in a strategic location
2. The north did not want to lose Fort Sumter because it was controlling the imports and exports of the country and the southerners relied heavily on them b/c the Southerners would trade cotton and tobacco for daily needed supplies
3. If North lost the fort it would make Lincoln look like he could not control federal property
4. Anaconda Plan