AFAIK, the time line of all canon FM games goes like this (
From GFAQs thread):
2034 - African Conflict (Front Mission Alternative)
2070 - 1st Huffman Conflict (FM5 intro, referenced throughout FM1)
2086 - Huffman Crisis (Front Mission Border Madness)
2090 - 2nd Huffman Conflict (Front Mission 1st)
2096 - Venezuela coup d'etat, Madeira Island invasion (Front Mission 4)
2097 - Cambodia coup d'etat, Laos coup d'etat (Front Mission 5)
2098 - 1st Alordesh coup d'etat (Referenced in Front Misssion 2)
2102 - 2nd Alordesh coup d'etat (Front Mission 2)
2112 - M.I.D.A.S. theft, Japan coup d'etat, Philippines coup d'etat, Da Han Zhong coup d'etat (Front Mission 5, and Front Mission 3)
Its good to note that Front Mission touches up on events from the First Huffman Conflict until the beginning of Front Mission 3, though its ending reaches up to 2125.
Trace can prolly give more info on the details as he has played FM for the DS, dunno if he played both the UCS and OCU scenarios though. FM1 is prolly the most heavily referenced game in FM5 largely because the central plot of FM5 revolves around the cause of the Second Huffman Conflict, when majority of FM1 takes place.