Question

checkpoint 19
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what was once the western border of the united states?
○ appalachian mountains
○ laurentian mountains
○ sangre de christo mountains
○ allegheny mountains
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Explanation:

To solve this, we analyze each option:

• The Appalachian Mountains were once considered a western boundary - like region in the early US expansion context (as the US initially expanded westward from the east coast, with the Appalachians marking a western frontier - like area in early history).
• Laurentian Mountains are in Canada, not relevant to US western border history.
• Sangre de Christo Mountains are in the southwestern US, not a historical western border marker.
• Allegheny Mountains are part of the Appalachian system but the broader Appalachian range is the key here for the historical western border context.

Answer:

A. Appalachian Mountains