A history of conflict and a present bedevilled by recession, drug-trafficking and illegal immigration should be reason enough to make relations across the Rio Grande decidedly fraught.

由于历史的冲突和目前让人困扰的经济衰退，贩毒和非法移民有足够的理由对跨越格兰德河的关系无疑变得更加让人担忧。

youdao

One reason for the speech was the state of Arizona's recent passage of its own law against illegal immigration.

VOA: special.2010.07.03

The lack of a legal visa category for the jobs most illegal immigrants fill is a core reason for illegal immigration.

FORBES: Too Few Work Visas in New Immigration Bill

Today, there are few legal avenues for lesser-skilled foreign workers, which is a prime reason for illegal immigration.

FORBES: Colbert Hits the Mark in Hill Testimony

One reason appears to be reduced immigration, both legal and illegal, because of diminished job opportunities and more effective border enforcement.

ECONOMIST: Troubling trends behind the falling unemployment rate