The Collaborative International Dictionary of English v.0.48:

Subjugation \Sub`ju*ga"tion\, n. [Cf. F. subjugation, LL.
   subjugatio.]
   The act of subjugating, or the state of being subjugated.
   [1913 Webster]

WordNet (r) 3.0 (2006):

subjugation
    n 1: forced submission to control by others [syn: subjugation,
         subjection]
    2: the act of subjugating by cruelty; "the tyrant's oppression
       of the people" [syn: oppression, subjugation]
    3: the act of conquering [syn: conquest, conquering,
       subjection, subjugation]

Moby Thesaurus II by Grady Ward, 1.0:

77 Moby Thesaurus words for "subjugation":
   Waterloo, absolutism, adoption, appropriation, arrogation,
   assumption, beating, bond service, bondage, captivity, collapse,
   colonization, conquering, conquest, control, crash, deathblow,
   debacle, debt slavery, defeat, deprivation of freedom, destruction,
   disenfranchisement, disfranchisement, domination, downfall,
   drubbing, enslavement, enthrallment, failure, fall, feudalism,
   feudality, helotism, helotry, hiding, indent, indentureship,
   lambasting, lathering, licking, mastery, occupation, overcoming,
   overthrow, overturn, peonage, preemption, preoccupation,
   prepossession, quietus, requisition, restraint, ruin, serfdom,
   serfhood, servility, servitude, slavery, smash, subdual, subduing,
   subjection, takeover, taking over, thrall, thralldom, thrashing,
   trimming, trouncing, tyranny, undoing, usurpation, vanquishment,
   vassalage, villenage, whipping