Crop breeding in the 20th century led to increased yields but had limitations. Genetically modifying crops allows introducing genes across species and has increased yields for some crops grown in the US since the 1990s. However, there has been a campaign in Europe against GM crops based on environmental and food safety concerns, though analyses find some claims are erroneous. Reasonable caution is still advised with new technologies. Issues of global trade and justice must also be considered separately from the GM technology.