Currencies tend to trend more and fluctuate less violently unlike stocks which behave pretty much the different way. The reason for this is not hard to understand. Currencies trend depending on the countries' foreign and economic policies which are macro economic in nature and the currency pairs take fairly long enough time to react to any change in policies. Where as stock movements are more or less determined by microeconomic factors and market sentiments.

Euro/US Dollar: On Par at the Beginning
When Euro was brought into force its exchange rate was set officially at 1 USD a Euro. At that time there existed hardly any difference between the economies of US and the European Union. US had a GDP of $11.0 billion and European Union was pretty up close there at $10.5 billion. While US economy was growing at a good rate of above 3% per annum Europe was a bit sluggish and recorded slightly over 1.5%.

Gradual Shift In Favor Of Euro
But this was not coming in the way of Euro's gradual march ahead of US Dollar. Look at other key economic factors for yourself. US had a deficit budget and the balance of trade was negatively skewed against US while the European Union had some of the seriously good parameters in exact contrast to that of the US's. The trade balance sheets looked healthy and strong standing on the near equal GDP.

During this period India, China, Russia and Brazil were making big strides in economic growth and Europe was gaining position in their trade partnerships shifting the forex currency in Euro's favor. At a time when their reserves were growing by leaps and bounds, US Dollar was sliding continuously which contributed to the conversion of their reserves into Euro, but partially.

How Does The Market React To This?
Euro/USD is by far the biggest forex pair which accounts for $1 trillion every trading day. With so many changes in the world economic scenario and the notional trades in between the two currencies still commanding 1/3rd of the currency market, the US dollar trended constantly over the years.

The firm trend may not be apparent in short term price charts but a relatively long period chart such as 2-3 years would clarify Euro's constant gain against USD. Till recently cross currency payments were, say for Japanese payments to Germany, first by converting Yen into USD and then USD into Euro. Now such a necessity doesn't arise for payments.

All these things mean that the trends are going to continue for long unless there is a strong reason.