> Not recent at all.
The illegal crossings by refugee applicants are recent.
> The United States has received waves of refugees for centuries.
Yes, but under the modern legal asylum regime, there has been no reason for those seeking refugee status to make border crossings other than at regular ports of entry, because there is a legal process for them to apply for asylum at such ports and it's in their interest to follow it. Until, that is, the government actively prevented them from doing so, which is a recent phenomenon.
> What sets a lot of those refugee groups apart is that they were fleeing war and persecution
The recent waves are also fleeing war and persecution (as in many of the previous waves, war that the US is directly involved in, this time, I signficant part, the Central American drug wars, which—unlike the largely metaphorical war on drugs in the US—are actual wars.)