Answer:
High numbers of immigrants can be a burden on the economy.
Border walls protect against terrorism.
Explanation:
The author of "Strong borders build strong nations" is in favor of walls at national borders, because he believes that this would prevent the entry of immigrants and the decrease in the number of immigrants would make the country stronger. The author tries to provoke fear and disgust at the presence of immigrants in a country and for this reason he states that the use of walls at the borders would prevent immigrants from overloading a country's economy, in addition to preventing terrorist attacks, which in the author's opinion , are provoked by immigrants, generally.
