Allied fetchlands were initially printed in Onslaught and therefore not legal in Modern.
Their reprint in Khans of Tarkir made them legal in Modern and also dropped their price, making them more afordable.
Fetchlands are the base of the manabase of every modern multicolored deck, get a playset of each as soon as you can!
a must have in any green/red deck, and even playable in standard!