The Block-Schwenk Collective 
Sometimes, weapons can be worse than useless.
Sometimes, allies can also be worse than useless.
Military tactics should conform to military realities, and not a nation's self-image.
Do not needlessly make enemies.
In a major war for survival, there's no "risk averse" strategy.
Note: Part Four was written in February, 2002. It will shortly be updated to address current circumstances.
I talk of today's applications as they relate to the United States. This is not because I think the United States is worse than other countries, but rather because I live in the United States (as do more of the readers), and am thus is a better position to influence policies of my own country, as well as more knowledgeable of them.
Lessons drawn from World War I are all going to be a bit general, as the international situation today is vastly different from that of 1914. Specifically, the United States is a hyperpower, with a military budget higher than that of countries #2-#17 combined. This is different from the roughly equal balance of power in Europe in 1914. Furthermore, the presence of nuclear weapons means that there will never be another "total war" like World Wars I and II, as today total war would mean nuclear war, which would be short and beyond catastrophic for all sides, whereas in 1914 all sides genuinely hoped to profit from war.
Germany's decision to build a large surface navy hurt it three ways:
Before the war, this arms race resulted in a souring of relations with the British Empire.
The cost to Germany of this navy could have been used in two more army corps, which just might have made a decisive difference vs. France in 1914.
At the end of the war, the German collapse was sparked by a mutiny among the German sailors, when the navy was order to sally forth for "one last glorious battle."
During the war, the German navy spent almost all of its time in port. While it sank a few allied warships, this did not make a significant contribution to winning the war. Thus, Germany would have been better off without a surface fleet.
Nuclear weapons today are probably the best example of weapons that reduce a state's security. Before 1945, the United States was essentially impregnable, with Oceans east and west, and friendly, weak neighbors north and south. In the late 1940s the United States decided to make nuclear weapons the cornerstone of its defense, rather than agree to a meaningful international ban, or even a combination of nuclear and conventional forces. (Specifically, the West did not keep enough soldiers in Europe to stop a Soviet attack in the 1950s, instead using the nuclear threat). As a result, within 15 years the United States had gone from being an impregnable fortress to 30 minutes away from total annihilation.
More recently, India, previously the dominant power in South Asia and fundamentally secure, is now threatened with nuclear weapons. Any time a nation goes nuclear, the other nuclear states immediately aim weapons at it as a deterrant. The safest place in Earth is probably New Zealand, which has no nuclear weapons.
It's an open question whether nuclear missile defense will enhance or reduce security. There are good arguments on either side, but the point is that the debate should take place. We should not automatically assume that every new weapon makes us safer.
In a similar vein, the Clinton (and Bush Jr.) administrations' refusal to sign on to the treaty banning land mines is likely to get American soldiers killed while contributing nothing to our security: our military is strong enough to win any frontal fight, but land mines always cause incidental casualties, without any good way to absolutely defend yourself, unless your soldiers stay holed up in their bases, which can defeat the purpose of their being deployed.
While some weapons are worse than useless, others weapons are just plain useless. It is hard to imagine our battleships (which were obscelescent in World War II) or our heavy tank divisions (which have no comparatively armed enemy, and are slower and less effective than aircraft) being employed in any foreseeable conflict.
Russia's alliance with the small state of Serbia, and Germany's alliance with the weak state of Austria-Hungary, resulted in World War I starting in the first place, which ultimately led to the collapse of their governments.
Coaxing Romania into the war was a colossal disaster. Rumania was quickly overrun, at which point the Central Powers had full access to its resources. The allies would have been far better off had Romania stayed neutral.
Today, NATO is considering admitting the three former Soviet Baltic republics of Estonia, Latvia, and Lithuania. These states are all very small and poor, unable to contribute significant soldiers to the alliance. However, by their proximity to Russia, as well as the large numbers of ethnic Russians in these states (who face discrimination in Estonia and Latvia), their admission to NATO has the potential to severely sour our relation with Russia, a state with thousands of nuclear weapons. Similarly, our de facto alliance with Taiwan has the potential to get us into a conflict with China, another nuclear-armed state, while it is difficult to see what proportional benefit we derive from having that country as an ally (as opposed to a friendly neutral).
This was more of a lesson for World War Two: the states which lost in World War One were, in general, in better shape to fight World War Two, as they retained their ethnic base while shedding themselves of the border areas which contained many ethnic minorities, often associated with other countries. Bulgaria and Germany are good examples of this. By contrast, the multi ethnic state of "Greater Serbia," a.k.a. Yugoslavia, was smashed by the German armies within a couple of weeks.
The best case here applies to the Israeli occupation of the West Bank and Gaza, areas that, with large populations of hostile minorities and no significant resources, are clearly worse than useless.
If Israel continues to hold onto those territories, it has 3 options, all bad:
1. Grant full citizenship to the inhabitants. If this is done, Jews would no longer be a substantial majority, and would be a minority within a couple of decades. Moreover, many of these new citizens don't believe in Israel period, so Israel would lose the unity of purpose that had previously enabled it to defend itself successfully from 1948 on.
2. Continue the occupation as is: At best, we will continue to see the slow-burn of terrorism, murder, and retaliation waste lives, and sap national energies badly needed in other areas. Given the increasing presence of weapons of mass destruction (nuclear, chemical, biological), the costs of terrorism have the potential to increase astronomically.
3. Expel most if not all of the Palestinians from the territories. This would probably start a war, and at minimum would lead to Israel's diplomatic and economic isolation, plus probably more terrorism.
The French military refused to give their soldiers camouflaged uniforms, which resulted in thousands of needless casualties. Similarly, their insistence that French regular soldiers could outfight German soldiers (despite, or maybe because of, their thrashing less than 50 years before), while reserves were useless, nearly cost them the war in the opening weeks.
The military reality of today is that we are more likely to face terrorists and secret agents than marauding divisions. Indeed, in the past 50 years big wars of either annihilation or meant to grab territory have become increasingly rare, most conflicts today being civil wars, sometimes with a side supported by another country. Meanwhile, too much of our military budget is frittered away on the heavy warships, advanced fighter and bombers, and heavy fighting divisions designed to fight an updated version of World War Two (or One) all over again, a war that will never happen, while at the same time our intelligence services have been neglected.
The great irony German strategy is that it kept assuming that it would lose the war as it was, when in fact it could have won. Then in a gamble for temporary advantage it brought enemy after enemy into the war against itself. Germany could have smashed Russia while holding the line vs. France, instead it invaded France through Belgium, thus bringing England into the war. Then, just as Russia was collapsing and the western allies were approaching exhaustion, the unrestricted submarine warfare campaign was launched in a desperate bid to knock out England, thereby bringing the United States into the war.
In the 2002 State of the Union speech, President Bush referred to the governments of Iraq, Iran, and North Korea as being an "Axis of Evil," despite the fact that relations with the latter two have been improving recently (Iran was practically an ally in the recent action in Afghanistan). Calling other nations "evil" does not help secure what you want by diplomatic means, and by lumping all three nations into a group, it will make it that much harder to take action against any one of them, as any allies of any of them will assume that they're next on the list.
Germany decided to send its armies if its "right wing" through Belgium, knowing that that would possibly bring the British Empire into the war, in an "all or nothing" bid to knock out France during the first 40 days of the conflict. However, two army corps (roughly 25% of the right wing's strength) were pulled off the German right to fight the Russian armies who had penetrated East Prussia. (By the time these corps arrived on the Eastern Front, the Russian armies had already been defeated.) Similarly, the right wing was never reinforced in strength, while reinforcements were sent en masse to the German left wing.
By attacking everywhere and wanting numerical superiority on every front, the German high staff ensured that the German right wing would be of insufficient strength to outfight the French armies near Paris, and Germany would thus face a long, two-front war-precisely the war it had wanted to avoid.
The Soviet Union made a similar error after World War II. Given the fact that the Soviet armies never fought a major offensive campaign after World War 2, its interests would have been perfectly well served by a smaller military sufficient to dominate its region and deter attack. By seeking to match the NATO forces on all fronts, despite a much smaller resource and industrial base, it ended up spending 25+% of its national output on the military, which directly led to its economic and political collapse.
The United States spend a much smaller percent of its national income on the military, closer to 4%. This level can probably be sustained indefinitely, though at the cost of retarding other types of development. The fact that our allies spend even less has given them an economic advantage. The United States could spend 20% of what it currently does and still have the strongest military in the world, more than enough to deter any attack.