▶ Watch Video: Air travel delays and cancellations hit travelers over July 4 weekend

It was a tough holiday weekend, as airlines canceled 1,200 flights Friday, another 1,200 Saturday and about 300 and 225 on Sunday and Monday, July 4, respectively. Delayed flights were also in the thousands, with ground stops — all traffic halted — at airports like Denver, Miami, Atlanta, Newark and Minneapolis. And travelers weren’t delayed just by airlines and on the tarmac, but at many passenger security checkpoints at U.S. airports.

Overseas, major delays and cancellations occurred at airports like Lisbon, Frankfurt, Dublin and Amsterdam. The situation in Amsterdam was so serious, the Netherlands issued an unprecedented order telling airlines to suspend selling any more tickets between now and the end of July. That almost immediately drove up the price of airfares — which are now sky high. On many trips within Europe, the train is rapidly becoming a very attractive option.

Delays and cancellations are likely to continue, as airlines can’t either find workers, or if they do, train new employees fast enough.

The general rule for delays and cancellations is that for every 12 hours there’s a schedule disruption, it takes about 36 hours to get crews back on schedule and planes back into sequence. But this time, airlines are not dealing with a single incident, like weather. It’s a recurring problem due to staff shortages and overscheduled airlines. Airline schedules may not stabilize until after Labor Day, when a combination of reduced demand and newly hired — and trained — airline employees begin working.