Question

In Letter to a Citizen of Kentucky, an excerpt:
When, in March and May and July, 1862, I made earnest and successive appeals to the Border States to favor compensated emancipation, I believed the indispensable necessity for military emancipation and arming the blacks would come, unless averted by that measure.

When Lincoln refers to that measure, what specifically does he mean?
a. Arming the blacks
b. Compensated emancipation
c. Indispensable necessity
d. Wreck of government

Thanks for the help!!!!