It wasn't "allowed" as such; both territories were taken by force from Mexico during the Mexican-American War (1846-1848). See related questions for further details.
Yes. Mexico owned California, Arizona, New Mexico, Texas, Nevada, Utah, and parts of Colorado and Wyoming.However, Mexico lost all those territories at the Mexican-American War (1846-1848).
None were taken. The North won and forced the South to reunite in the Union.
Austira and Czechoslovakia
The cattle wasn’t taken to northern territories. In fact they were taken from the western plains to railroad hubs like Kansas City for shipment to the east for slaughter.
The Wilmot Proviso aimed to ban slavery in territories acquired after the Mexican-American War, specifically in the lands taken from Mexico. It was a controversial proposal that heightened tensions between the North and South over the issue of slavery expansion.
Nuevo Mexico. It is taken from the 'old Mexico' name. See related questions.
They would have to be cleared by custom agents in Mexico, but yes.
Mexico
Expenditure for which benefit is expected to be taken in one fiscal year from occurance of expenditure is called 'Revenue Expenditure" Expenditure for which benefit is expected to be taken for morethan once year is called 'Capital Expenditure'
Nahanni National Park, Nothwest Territories Canada.
Most of the US Imperial territory was taken from the Spanish in the Spanish-American War in 1898. Some other territories came as a result of negotiations with the other Great Powers and some more territories came as a result of World War II.