They don't have any choice but to defend it. Imo they won't successfully defend their title this year because the last time a team won back to back on the World cup was between 1960 to 1970.
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Nitrogensports looks like this. It's interesting that they favor Brazil over Germany or a lot of people bet on it which caused a massive movement on the Brazil line.
If you are looking at history you wont see a team winning them back to back in the near future, but in the past Italy and Brazil have won the title back to back, may be it is time for Germany to win their back to back titles, looking at the performance they have the team to defend it, i like to see the chances of Argentina and Portugal, Messi vs Ronaldo .