The Montagues in the March of Wales - a typical feudal career.

"Marcher Lords" in the March of Wales were those families that, in exchange for great grants of land, were supposed to insure that Wales remained under the control of the King. R.R. Davies, in Lordship and Society in the March of Wales, 1282-1400, describes the Marcher Lord career of the Montagues (he uses the e spelling):

"... most of the families of the March showed remarkable resilience and powers of recovery in the face of political disaster. From the point of view of the continuity of the family and of the inheritance it was another kind of calamity, and one from which there was no recovery, which created the greatest havoc - the failure of direct male heirs...

Whether it came suddenly or with an inexorable slowness, death without a direct male heir was a spectre which haunted every noble family. For it spelled the extinction of the house, the end of the landed inheritance as an entity, and either its amalgamation with another inheritance or its dispersal between co-heirs and co-heiresses. ... Nor was the absence of direct male heirs merely a domestic misfortune; it was often a matter of momentous significance in many other directions...

As one family after another failed in the male line, new ones took their place in the ranks of Marcher lords. They arrived, as usual, along the twin routes of marriage and royal support; indeed the routes were closely linked for the grant of the hand of an heiress was often an act of royal munificence. Among the most important new families which so appeared in the March in the fourteenth century were the Charltons, Despensers, Beauchamps, Montagues, Staffords, and (rather earlier) Hastings...

... another new Marcher family, the Montagues, owed their promotion entirely to the affection of Edward III towards William Montague (d.1344) , the first earl of Salisbury of his line. The lordship of Denbigh was bestowed on Montague in 1331 as a token of gratitude for his services to the king in effecting the downfall of the earl of March, its previous lord, in 1330. He had to pay heavily for the security of his title to the lordship; but it was no doubt worth it, for Denbigh with its gross income of 1,000 pounds per annum was one of the most desirable of Marcher lordships. Montague enhanced his standing as a Marcher lord in 1337 when he secured the reversion of the Montalt inheritance... from the queen mother... When he died in 1344, William Montague could feel confident that he had established the power of his house, both in England and in the March. Such confidence proved to be misplaced, for even the royal favour of Edward III was a fickle basis for a family fortune. That favour was not extended to the second Montague earl of Salisbury (d.1397) - not only was it withheld but, even more damagingly, it was bestowed on others who regarded themselves as hereditary claimants to the Montague lands. ... especially ... the young Roger Mortimer who recovered Denbigh from the Montagues in 1354. The Montagues retained Mold and Hawarden, but their career as major Marcher lords had been as brusquely terminated as it had been suddenly initiated in 1331...

Sources:
Lordship and Society in the March of Wales, Davies.

http://www.montaguemillennium.com/familyresearch/h_marcher.htm