In one of the bloodiest battles of the Civil War, fought at Sharpsburg

Hey, student26:

Good question on "as" vs. "than" here - because the GMAT does often test Comparisons, you should get used to one of the easiest ways that the test can manufacture an incorrect answer by twisting these idioms. For comparisons, there are three idiomatic constructions that you should make sure to know:

As many as (or "as much as") ---> Denotes equality (there is AS MUCH water in the Pacific Ocean AS in the Atlantic and Indian oceans combined)

So many that (or "so much that") ---> Denotes a "critical mass" (there is SO much pollution in the water THAT the beach is closed)

More than (or "less than" or "taller than" or anything with "-er than") --->Denotes inequality (there is MORE water in the Pacific Ocean THAN in the Atlantic)

With these structures in a Comparison-based questions, it's easy for the author of a question to just switch the last word of the construction to create a wrong answer:

"As many that"
"More as"
"So much than"

When you see one of these constructions, double-check to ensure that it's correctly structured, as the GMAT can easily switch that one word on you to create a wrong answer that's easy to overlook.