LET'S MAKE IT REAL

Wikipedia informs us about one of the US's big border wars.

The Mexican–American War, also known as the Mexican War, the U.S.–Mexican War, the Invasion of Mexico, the U.S. Intervention, or the United States War Against Mexico, was an armed conflict between the United States and the Republic of Mexico from 1846 to 1848 in the wake of the 1845 U.S. annexation of Texas, which Mexico considered part of its territory.

Combat operations lasted a year and a half, from the spring of 1846 to the fall of 1847. American forces quickly occupied New Mexico and California, then invaded parts of Northeastern Mexico and Northwest Mexico; meanwhile, the Pacific Squadron conducted a blockade, and took control of several garrisons on the Pacific coast further south in Baja California. Another American army captured Mexico City, and the war ended in a victory for the United States.

The Treaty of Guadalupe Hidalgo specified the major consequence of the war: the forced Mexican Cession of the territories of Alta California and New Mexico to the United States in exchange for $15 million. In addition, the United States assumed $3.25 million of debt owed by the Mexican government to U.S. citizens. Mexico accepted the loss of Texas and thereafter cited the Rio Grande as its national border.

The US has been grabbing other territories without popular election for a long time.  Check with the Indians just in case you still don't get it. 

Now let's imagine that Russia or China tries to play the same game.  They stir up the Mexicans with lots of money, say $5 billion for the project, and they even send in some mercenaries like Blackwater (name changed to Xe and then Academi) and their own intelligence operatives.  They also send in some of their 'diplomatic' people with bags of tamales to hand to the blossoming occupy effort in the streets of Mexico City that is demanding an end to their government and the return of lands stolen by the US.  One of the Russian diplomats gets caught in a conversation saying who Moscow wants to head up the new Mexican government.

Then on top of all that the Russians and Chinese send warships into the Gulf of Mexico and along the Pacific coast.  Russian warplanes begin flying out of Cuba and are bumping up along the US border.

When the US strongly reacts by mobilizing its own military the Russian and Chinese governments claim that the US is being provocative and overly aggressive.  Russia and China also demand that the US must return Texas, New Mexico, Arizona, and California back to Mexico.  Maybe even Colorado too.

All hell is about to break loose.