And the northern frontier was the most difficult of all.

He spent most of his time along Pennsylvania's northern frontier.

Georgia's northern frontier had been a partner in the new state's government.

In 1683, the Spanish on the northern frontier were vulnerable.

The situation was very different on the northern frontier.

The Russians invaded the northern frontier again in the 1680s.

The war had exposed the weakness of Rome's northern frontier.

He began his career on the northern frontier fighting the Xiongnu.

During the last months of the war he was in charge of the entire northern frontier.

The British, wanting political stability on their northern frontier, approved of the entire development.