Nations, like individuals, seem to establish patterns. Ebbs and flows of history often repeat themselves on semi-regular intervals, and whether it is hand-of-fate, mystical convergence or just plain-old natural progression patterns do emerge. The difference between individuals and nations, of course, is that the former is dictated by clocks while the latter is ruled by calendars.
The United States is no different in this regard, especially when it comes to war. It seems as though when we get involved in a military action the conflict recalls what happened 100 years before, which echoed what occurred 100 years before that... on and on.
The century cycle is not absolute, naturally, sometimes fluctuating by a decade or so, and the related conflicts are not precisely the same; that noted, there are enough similarities to establish a basic pattern. There have been hiccups in this cycle - the Korean War being the most prominent - but by and large this nation has fallen into patterns of war. Let's review, marching back in time from the current day.
A time period which breeds the beginnings of long-term, undefined conflicts; the 'Banana Wars' began in 1898 and stretched out through the mid-1930s, while The Indian Wars of the 1790's played out over several decades. These were engaged across multiple nations and territories, much like the current War of Terror is being fought.
This decade has also spawned brief, concise actions against specific, one-nation entities. Both the Gulf War of 1991 and the Spanish American War of 1898 were considered overwhelming victories with minimal loss of life or treasure. Each of these were preceded by years of relative peace, with minor military actions coming and going without much historical note. (The Barbary Wars - beginning in the 1790's - could technically fall into this category as well, though the length of this conflict, and what preceded it, would make such an inclusion a radical stretch.)
Defined by our deep involvement in civil wars, these time periods are some of the most brutal. Two these conflicts - the 1860's American Civil War and the 1770's American Revolution - were entirely wars of our own making, based largely on ideas, and fought on our own soil. There is much argument about how much the US contributed to the beginning of the 1960's Vietnam War, though the fact we were extensively involved in a civil war, one which was theoretically centered around ideas (democracy vs communism), remains undisputed.
Two major wars occurred during these decades. Both of them - World War Two in the 1940's and the Mexican War of the 1840's - not only involved attacks on U.S. territories, but the resulting victories gave birth to feelings of nationalistic pride amongst citizens. The earlier war inspired (for good or bane) a drive towards 'Manifest Destiny' and the conquering of a continent, while the later established the US as a global superpower.
As you can see, patterns do emerge when looking at the big picture. No, it is not an exact science, and no, I don't suggest a reason for said-patterns, I'm only noting that they do exist. If these hold out (which is no guarantee - patterns can be disrupted, after all, though it takes strong leadership and iron will to break them), we can get a general gauge of what's to come as time marches across the future history books.
Oh wait, I forgot one era, didn't I? - the decades of the 10's. These give us two conflicts which were considered especially vital at the times they were fought, but lost historical importance as time went on. This was due to three factors: the 'friendships' which grew out of them, the horrific conflicts that followed, and the fact that actions directly resulting from these wars helped foster the horrors to come decades later.
These two actions - the second war with Great Britain and World War One - began in 1812 and 1914, respectively. Something to bear in mind while listening to the war drums, as they beat in 2013.