Why would European countries want to build up their armed forces during the early 1900s prior to WWI?

Even before the war began in 1914, many countries in Europe had been expanding their armies and navies. Many leaders pushed for the steady build-up of their country's armed forces as a show of power. Most believed the best way to avoid trouble was to show enough military strength to discourage any attack.

From mexican american war , us gained new mexico.

12 days because 1/4 is 25% of 100 if 100 is equal to 1 pound then multiply 3 by 4 which equals 12