Complex sentence: By the 1960s, St. Clair Avenue had supplanted College Street as the center of Italian culture in Toronto; since then, many Italian Torontonians have moved to Toronto's suburbs.
Split into simpler sentences: By the 1960s, St. Clair Avenue had supplanted College Street as the center of Italian culture in Toronto. Within the past three decades, many Italian Torontonians moved to Toronto's suburbs.