The campaign by Bucharest-based BV McCann Erickson for Kandia Dulce, the confectionery manufacturer, was awarded the $10,000 prize created by Warc for the best case study of innovation in communications.
The winning campaign was built around a rebrand designed to provoke a groundswell of national sentiment for the struggling chocolate brand.
After supposedly being bought by a US group, Rom was relaunched in key stores as "American Rom" with the US Stars and Stripes replacing the Romanian flag's colours on its packaging.
TV and outdoor ads were used to create mass awareness of the change whilst the brand team monitored and fostered the ensuing public outcry on social media.
After several days, a TV-led reveal phase reassured consumers that Rom remained Romanian and its usual wrapping was restored.
This appeal to national pride resulted in massive earned media support, with the campaign reaching two-thirds of the Romanian population and helping Rom become its category favourite again.
The Warc Prize judges praised the scale, execution and daring of the campaign.
It edged out the Prize Runner-up, FARC Operation Christmas, a Lowe SSP3 campaign for the Colombian Ministry of Defence which attempted to persuade the nation's FARC guerilla force to demobilise.
Cases from Promote Iceland, Dettol, Febreze and Polident were also shortlisted for the Prize.
Jonathan Mildenhall, Prize chairman and Coca-Cola's vice president for global advertising strategy and content excellence, said: "Hands down the biggest idea, the most compelling execution and the most impressive results of the shortlisted cases were from American Rom. If all marketing platforms were this impressive, the world would definitely be a more interesting and dynamic place.
"But in Operation Christmas, we also had a very, very credible runner-up, and all in all we had a worthy shortlist."
Campaigns that effectively integrated multiple media found particular favour among the judging panel of industry experts. The winning campaign employed 12 main channels, and the six shortlisted papers used an average of 8.7. Across all of the entries received, the average number of main channels used was 7.6.
A total of 13 product categories were covered by the prize entries. The best-represented categories were automotive, on 12 cases, followed by household and domestic (9) and toiletries and cosmetics (8).
Nation by nation, India was the top market, accounting for 27 entrants. The US and UK came next, on 12 and 8 cases respectively.
To read the Warc Prize entries in full, visit www.warc.com/prize.
Data sourced from Warc