Washington (CNN) -- In a brief visit Wednesday to Toluca, Mexico, U.S. President Barack Obama will join his two North American counterparts to discuss environmental issues, security, driving economic growth through trade, and job creation.
The North American Leaders' Summit, which has come to be known as the "Three Amigos" summit, began in 1992 with President George H.W. Bush. Obama and Canadian Prime Minister Stephen Harper will visit Mexican President Enrique Pena Nieto.
Here are four issues among friends:
1. Butterflies and oil: While the Keystone XL pipeline continues to cause friction between the United States and Canada, the monarch butterfly is a sore spot in U.S.-Mexico relations.
Monarchs migrate to their breeding grounds in Mexico every year, but Mexican farmers are using a harmful pesticide to kill pesky milkweed plants. Monarch caterpillars depend on milkweed during their breeding season in Mexico.
Harper is expected to continue pressuring Obama to approve the Keystone XL pipeline, which would carry oil from Alberta, Canada, to the Gulf of Mexico. The two are scheduled to hold a bilateral meeting during the one-day summit to focus heavily on environmental and trade issues.
2. Canada cracks down on asylum-seekers: Pena Nieto's administration has complained loudly about Canada's imposing a mandatory visa rule specifically on Mexican travelers in 2009, facing a growing number of refugee cases where claims were denied.
Harper has said he would like to see the rule lifted, but he says Canada has to reform its own backlogged refugee system first. The Mexican government says the visa requirement is invasive and time-consuming, and blames it for a decline in the number of Mexican visitors to Canada. The Canadian Council of Chief Executives has urged the Prime Minister to lift the visa or simplify the process, making it similar to that of the United States. Pena Nieto and Harper signed an agreement on Tuesday that will expand air travel between the two countries.
3. U.S.-Mexican relationship strong but difficult: The relationship between the two countries goes beyond diplomacy -- there are commercial, cultural, and educational ties that account for more than $1.25 billion of trade and roughly 1 million legal border crossings each day. The U.S. has deported more illegal immigrants under Obama than in any previous administration -- 370,000 in 2013 alone, according to U.S. Immigration and Customs Enforcement (ICE).
Border security continues to be a divisive issue with any kind of immigration reform legislation in the United States.
4. Not everyone's happy with NAFTA: There are issues between Canada and Mexico in in the 20-year-old North American Free Trade Agreement. Harper on Tuesday called it "a very unbalanced relationship," saying trade flow has tilted toward Mexico and his government would like to bring it back into balance.