Collocations for frontier - noun

common
Neither country would guarantee the integrity of their common frontier.

eastern, northern, etc.
There were very few border controls on the south-western frontier.

Franco-Spanish, French-Spanish, etc.

cross
The army crossed the frontier in the middle of the night.

reach
control, defend, guard
The rebels control the frontier and the surrounding area.

controls, post
guard
zone

across the frontier
The weapons were smuggled across the frontier.

along the frontier
an army grouping along the frontier

at the frontier
There was an army checkpoint at the frontier.

on the frontier
people living on the German frontier

over the frontier
They were forced to retreat back over the frontier.

frontier between
the frontier between India and Pakistan

frontier with
France's frontier with Germany

wild
America's wild frontier

western

explore
tame
settle

province, settlement, town
mentality, spirit

final, last
new
next
technological

explore
Space is the final frontier for us to explore.

advance, expand, extend, open, push back
The scientists' work will push back the frontiers of physics.