How was the Mexican-American border different in the 1840s from the border today, according to Jones' account?

a. Mexicans had more reasons to guard the border then, the U.S. has more serious reasons to guard the border today.
b. Borders back then were even more guarded than today.
c. Borders back then were only guarded in times of war.
d. Even though the border is more militarized today, it is not as deadly as it was back in the 1840s at the end of the Mexican-American war.