One possible negative impact of global trade, both at the time and today, is the spread of disease and invasive species carried in these goods. When two countries trade with one another, specifically when it comes to agricultural products like livestock, fruit, and vegetables, they can also inadvertently trade the diseases and other invasive species, such as insects, that live among these products.
The Silk Road and other Eurasian trade routes were a contributing cause to how plagues spread so quickly to Europe from Asia, and today we see issues with tainted meat and other infected products being exported and affecting people around the world.