The dollar reached a peak against major currencies in 1985, then slid 52 percentage points over the next 25 years. It's been rising since August 2011, yet has recovered only 8 percentage points of that 52-point slide. Of course, there’s no assurance that the dollar will regain its 1985 peak, yet there are concrete reasons to expect it to remain strong over the long haul.
The dollar has been the primary trading and reserve currency since World War II and is likely to remain so for decades. Rapid growth in the economy and per-capita output weigh in the dollar’s favor. American financial markets are broad, deep and transparent, as is the economy. Despite the dollar's decline since 1985, its credibility is substantial.
And there is no real substitute for the dollar as a global currency.