1. Early gets moving faster, Grant's reinforcements don't make it to Washington DC on time, Early takes Ft. Stephens, and Lincoln (in the vicinity of Black troops) is lynched by the Confederate troops after the battle at the beginning of June.
2. Hamlin is now president of the US and was selected by the delayed Republican convention as the 1864 Presidential candidate. The US is severely pissed that the Confederacy doesn't seem to get the idea that they are defeated or that they should pay even minimal attention to the laws of war relating to Black troops.
3. The US votes in a Republican regime with an even larger majority and a much less comprimising attitude. The Union raises many more Black regiments and pays them the same wages as White regiments.
4. The Confederacy develops an even less compromising attitude in response, and is more resistant to the Union assault. Large numbers of wealthy slave owners are conscripted to join the troops. Having more than 20 slaves no longer exempts you from service.
5. The tranAmerica railroad was postponed because the war is lasting longer and the political situation postLincoln is taking time to stabilize. The first railroad act in 1862 was insufficient to enable the railroads to be built and in OTL the second railroad act of 1864 was signed by Lincoln on July 2nd. The line constructed at Omaha becomes a minor branch railroad.
5. The US still wins, but only after pursuing the Confederacy into Florida and Texas with the newly raised Black regiments front and center during the guerilla campaigns.
6. Voting rights for Confederates are suspended till five years after the duration of the war in all the Confederate states, and the White lowland Confederacy is effectively disenfranchised until the 1872 elections.
7. Since the Black regiments are the newest regiments they wind up as the occupation forces when the long service White regiments are mustered out and the veterans go home.
8. Black majority states like Louisiana and South Carolina are joined by Florida and Texas as Black troops cycle through the occupation regiments and settle there in the postwar period.
9. Texas is split into five states (with eastern New Mexico) as part of the effort to ensure that the Republicans maintain control of the Senate in the elections of 1872. There are now 16 Black Senators out of 88. Colorado, Dakota, and Nebraska are also admitted, as is Utah.
10. Texas winds up as the route for the transAmerican railroad as the political situation shifts with the newer Senators included in the patronage games. Southern California develops faster than in OTL because the railroad ends at San Diego instead of San Francisco.
11. Black migration continues along the railroad into Arizona. The Arizona copper mines and coal mines are developed sooner with the increased transport capability and demand. Now that the Black population of the South has someplace to go they are encouraged by the White population to go there.
12. The US builds irrigation dams and sets up irrigation districts considerably faster than in OTL because of the increased Black voting representation in the Congress and the Senate. Local districts are set up by the states as in OTL. This occurs sooner than in OTL because the railroads were built sooner and the population built up sooner.
13. The US buys the lower reaches of the Colorado delta from Mexico, along with Baja California. the irrigation ditches are flowing into the Sea of Cortez instead of the Salton Sink, so the Salton Sea does not form and the Salton Sink becomes a major salt and sodium sulfate supplier. This area is also settled by Black irrigation farmers, gaining yet another two Black Senators on statehood in 1880. Idaho and Wyoming split Montana between them and are also admitted.
14. Black/White differences in the South are no longer politcally important. There aren't enough Black people left to make a difference in patronage. Discrimination by government dies out. The South is not Solid and regional differences become more important by 1900. Black Senators are now Western and Southern Senators in the voting blocks, Confederate Senators are now Southern, Upper Southern, and MidAtlantic Senators in the voting blocks.