The Mexican–American War, also known as the Mexican War and in Mexico the American intervention in Mexico, was an armed conflict between the United States of America and the United Mexican States (Mexico) from 1846 to 1848. It followed in the wake of the 1845 American annexation of the independent Republic of Texas, which Mexico still considered its northeastern province and a part of its territory after its "de facto" secession in the 1836 Texas Revolution a decade earlier. 

After its Treaty of Córdoba with obtaining independence in 1821, from the Kingdom of Spain and its Spanish Empire as New Spain for the past 300 years, and a brief experiment with a monarchy government, Mexico became a republic in 1824. It was characterized by considerable instability, leaving it ill-prepared for international conflict only two decades later when war broke out in 1846. Native American raids in Mexico's sparsely settled north in the decades preceding the war prompted the Mexican government to sponsor migration from the U.S.A. on its northeast border (since 1803 with the Louisiana Purchase from the French Empire (France) of Emperor Napoleon I) to the Mexican province of Texas to create a buffer. However, the newly-named "Texians" revolted against the Mexican government of President / dictator Antonio Lopez de Santa Ana, who had usurped the Mexican constitution of 1824, in the subsequent 1836 Texas Revolution, creating a republic not recognized by Mexico, which still claimed it as part of its national territory. In 1845, the Texan Republic agreed to an offer of annexation by the U.S. Congress, and became the 28th state in the Union on December 29 that year.
When did Mexico become a republic?
So, how long after that was the Mexican-American War?
Who were the parties to the Mexican-American War?
What was the time period of that war?
Did the United States annex anything?
What?
Did Mexico think it was part of Mexico?
What part?
When was the Texas Revolution?
Was Mexico ever a monarchy?
How long was it?
Before when?
Who was raiding Mexico in the north?
What was Mexico's attempted solution to those raids?
When did Texas become a US state?
What was it just before that?
What was the offer it took up from the US then?
Which French person was party to the Louisiana Purchase?
When was that?
What was a new name for Texans?
1824
Mexico became a republic in 1824
22 yearrs
The Mexican–American War, also known as the Mexican War and in Mexico the American intervention in Mexico, was an armed conflict between the United States of America and the United Mexican States (Mexico) from 1846 to 1848
United States of America and the United Mexican States
an armed conflict between the United States of America and the United Mexican States
1846 to 1848
an armed conflict between the United States of America and the United Mexican States (Mexico) from 1846 to 1848
Yes
In 1845, the Texan Republic agreed to an offer of annexation by the U.S. Congress
the independent Republic of Texas
the 1845 American annexation of the independent Republic of Texas
Yes
Texas, which Mexico still considered its northeastern province and a part of its territory 
northeastern province
Texas, which Mexico still considered its northeastern province and a part of its territory
1836
the 1836 Texas Revolution a decade earlier
Yes
a brief experiment with a monarchy government
brief
 a brief experiment with a monarchy government
1824
a brief experiment with a monarchy government, Mexico became a republic in 1824
Native Americans
Native American raids in Mexico's sparsely settled north
to sponsor migration from the U.S.A. on its northeast border
Native American raids in Mexico's sparsely settled north in the decades preceding the war prompted the Mexican government to sponsor migration from the U.S.A. on its northeast border
1845
In 1845, the Texan Republic agreed to an offer of annexation by the U.S. Congress, and became the 28th state in the Union on December 29 that year.
Texan Republic
In 1845, the Texan Republic agreed to an offer of annexation by the U.S. Congress
offer of annexation
In 1845, the Texan Republic agreed to an offer of annexation by the U.S. Congress
Emperor Napoleon I
the Louisiana Purchase from the French Empire (France) of Emperor Napoleon I
1803
1803 with the Louisiana Purchase from the French Empire (France) of Emperor Napoleon I
Texians
the newly-named "Texians"