This is pokeweed (Phytolacca americana), a North American native plant with a very wide range. Pokeweed is widely regarded as a common weed. It prefers moist meadows in woodland openings, thickets, woodland borders, edges of marshes, pastures, abandoned fields, vacant lots, neglected gardens, and areas along roadsides, and railroads. The foliage and stems of pokeweed are somewhat toxic and bitter, particularly when the plants are mature. The berries are also slightly toxic, although birds (and possibly some mammals) enjoy some immunity from adverse effects. More information here: http://www.illinoiswildflowers.info/weeds/plants/pokeweed.htm