I think if the United States breaks up, it could actually be into many countries, ranging from city-states like Chicago to swaths of several contagious states:

1) Miami area
2) South Florida
3) Central Florida
4) Florida north of Daytona, Alabama, Mississippi, Louisiana, Arkansas, Eastern Texas, Georgia south of the Atlanta area, some parts of West Tennessee and East Tennessee
5) Atlanta area
6) Nashville area
7) Downstate Illinois, Kentucky, Indiana, and Ohio (may lose some areas along the Michigan and Missouri borders(
8) Chicago area
9) Memphis area
10) South Carolina
11) Charlotte
12) North Carolina
13) West Virginia and rural Virginia
14) Coastal Virginia
15) Northern Virginia, DC, Delaware, Maryland, New Jersey, New York City area, Philadelphia area, and New England
16) Central Pennsylvania and Upstate New York
17) Pittsburgh area
18) Milwaukee-Madison corridor
19) Wisconsin and Minnesota outside the Twin Cities
20) Twin Cities area
21) Saint Louis area
22) Iowa and Missouri (excluding Saint Louis and Kansas City)
23) Kansas City area
24) Kansas, Oklahoma, Nebraska, South Dakota, North Dakota, Montana, Wyoming, Utah, Nevada outside of Las Vegas and Reno, Idaho, Eastern and Southwestern Oregon, Eastern Washington, and some counties in Northern California
25) Colorado, New Mexico, and the El Paso area
26) Austin-San Antonio
27) Dallas-Fort Worth
28) Houston area
29) Rio Grande Valley
30) remaining portion of Texas
31) Portland area
32) Seattle area
33) Remaining portion of California
34) Hawaii
35) Alaska