Final answer:
Delta Airlines' entrance into international competition, especially to Europe, aligned with the broader industry changes following the Airline Deregulation Act of 1978, which allowed for greater expansion into international territories.
Step-by-step explanation:
The question pertains to the period when Delta Airlines began its international competition, specifically to European destinations. Looking at the historical context provided by the Airline Deregulation Act of 1978, this legislation allowed airlines to set their own airfares and schedules, leading to a significant overhaul of the industry. Although the detailed answer does not provide a specific date for when Delta began flying to Europe, the deregulation period marked the beginning of increased competition and expansion for airlines, including Delta's push into international markets.