beachhead

(noun) a bridgehead on the enemy's shoreline seized by an amphibious operation. Example: "The germans were desperately trying to contain the anzio beachhead."

(noun) an initial accomplishment that opens the way for further developments. Synonyms: foothold. Examples: "The town became a beachhead in the campaign to ban smoking outdoors." "They are presently attempting to gain a foothold in the russian market."