Investors tend to remember the biggest crisis events even after years have passed, and the 2010 Greek sovereign debt crisis that put the entire common European currency in danger still looms large in the collective investor consciousness five years later. Yet even as elections in the Mediterranean nation over the weekend changed its political environment and led some analysts to consider the long-term impact of changing conditions throughout the continent, U.S. investors responded Monday morning with a yawn, as the Dow Jones Industrials (DJINDICES:^DJI) had lost just 30 points as of 11:35 a.m. EST.

When you consider just how much markets responded to the first Greek crisis, it's surprising to see the lack of reaction this time around. An unlikely coalition between extreme parties on both ends of the political spectrum helped move Alexis Tsipras into power as Greece's new prime minister. His Syriza party and the Independent Greeks Party found common ground in opposing all the massive cost-cutting measures that the national government has accepted in order to qualify for financial assistance from the European Union and the International Monetary Fund. By showing that the public's tolerance of economic moves is limited, Greece could once again prove to be the linchpin that leads to similar demonstrations of populist power in other eurozone nations with weak economies.

Source: Flickr user Pedro Szekely.

Yet one reason why U.S. investors are largely ignoring Greece could be simply that Europe has far greater issues to deal with right now. Sluggish economic conditions prevail over much of the continent, and the value of the U.S. dollar climbed briefly above the 90 euro cent mark for the first time since late 2003 before dropping back slightly. As the European Central Bank begins its own adventure with quantitative easing, investors there are concerned about whether the measures will succeed, and that in part has driven Europeans to invest instead in U.S. stocks, bolstering our markets.

Meanwhile, some other hot-button issues have started to fade into the background. Oil prices are holding in the high $40s per barrel as OPEC leaders now believe that crude might well have hit bottom. OPEC secretary-general Abdalla El-Badri went even further, suggesting that if exploration and production companies cut off their investment in finding new supplies because of the price drop, prices could eventually spike to record levels. In response, the Dow's energy stocks moved higher, with Chevron (NYSE:CVX) leading the way with gains of nearly 2%.

U.S. investors shouldn't ignore Greece entirely, as it is a good example of how European sentiment can ebb and flow over time. Yet nothing that's happening right now in Greece is likely to have a huge impact on the powerful forces that have supported domestic stock markets in recent months, and any Greek concerns will need to build before they can truly threaten the U.S. bull market.