* Serbian Interior Ministry (labeled on map) moved in close conjunction with army after March 24.
Sources: U.S. Defense Dept., U.S. Intelligence
(Maps by Dita Smith, Robert Thomason, Louis Spirito and Robert Dorrell for The Post and Paul Compton for washingtonpost.com)
BUILDUP: In January, major 3rd Army groups move south from Nis and Kraljevo, and troops in Kosovo move out of their bases.
By late March, 27,000 army and special police are inside Kosovo, with about 300 tanks and 150 artillery pieces.
Another 14,000 troops mass along Kosovo's border with 100 tanks, 150 artillery pieces and 100 armored personnel carriers.
Special police and irregular units concentrate around Mitrovica and in southwestern Kosovo, in an area between Pec, Djakovica, Suva Reka and Velika Hoca.
Racak: On Jan. 15, interior police and irregulars cooperate in massacre of about 45 civilians in Racak; it sets tone for later killings.