Lathrop Gage and Gray Plant Mooty will combine next year to form Lathrop GPM, the firms announced Thursday, creating a new 400-lawyer firm and extending a streak of Midwest law firm mergers.

The deal, effective Jan. 1, 2020, will unite Kansas City, Missouri-based Lathrop Gage’s 240 attorneys with Minneapolis-headquartered Gray Plant Mooty’s 155 lawyers. With 14 offices—concentrated in the Midwest but including coastal outposts in Boston, Washington, D.C., and  Los Angeles—Lathrop GPM will have a deeper presence in the heartland as well as a broader national reach, the firms said.