The global sports betting industry has been characterized over the past five years by equal parts growth and consolidation.

The revenue of the top five companies have tripled, driven by 70% growth in industry revenue and an 80% increase in concentration, or those five firms buying smaller rivals. Just last week, Barstool Sports backer Penn National Gaming Inc. agreed to buy Score Media & Gaming Inc. for about $1.74 billion. This week, DraftKings Inc. agreed to buy Golden Nugget Online Gaming Inc. for about $1.56 billion. How long will this trend continue and where will it lead?

We have an historical parallel for what is happening. In the early 20th century, sports bookmaking in the U.S. was a strictly local business. But with the end of Prohibition in 1933, the criminal enterprises that law created had to find new sources of revenue and turned to drugs, prostitution and gambling. Over the subsequent two decades, local bookmaking gave way to a single national organization quoting a unified "Vegas line” everywhere. Local bookies became franchisee order takers.