What does the abbreviation for the latin phrase anno domini refer to?

Anno Domini (in Latin 'in the year of the Lord'), abbreviated as AD, is a calendar indicator that indicates that the preceding figure is counted from the Christian year of the birth of Jesus Christ (Jesus of Nazareth), considered the beginning of the Christian era.

cruel, heartless

explanation:

the  seven  days  battles  were  a series of seven battles over seven  days from june 25 to july 1, 1862, near richmond, virginia,  during  the american civil war. the  seven  days ended with mcclellan's army in relative safety next to the james river, having suffered almost 16,000 casualtiesduring  the retreat.