One disadvantage of the phalanx was that it was only effective when fighting in large, open spaces, which left the Romans at a disadvantage when fighting in the hilly terrain of central Italian peninsula. In the 4th century BC, the Romans abandoned the phalanx in favour of the more flexible manipular formation. This change is sometimes attributed to Marcus Furius Camillus and placed shortly after the Gallic invasion of 390 BC; it is more likely, however, that they were copied from Rome's Samnite enemies to the south, possibly as a result of Samnite victories during the Second Samnite War (326 to 304 BC).
What fighting formation would eventually replace the phalanx in battle?
manipular formation

A major consideration was the possible Soviet reaction in the event that the US intervened. The Truman administration was fretful that a war in Korea was a diversionary assault that would escalate to a general war in Europe once the United States committed in Korea. At the same time, "[t]here was no suggestion from anyone that the United Nations or the United States could back away from [the conflict]". Yugoslavia–a possible Soviet target because of the Tito-Stalin Split—was vital to the defense of Italy and Greece, and the country was first on the list of the National Security Council's post-North Korea invasion list of "chief danger spots". Truman believed if aggression went unchecked a chain reaction would be initiated that would marginalize the United Nations and encourage Communist aggression elsewhere. The UN Security Council approved the use of force to help the South Koreans and the US immediately began using what air and naval forces that were in the area to that end. The Administration still refrained from committing on the ground because some advisers believed the North Koreans could be stopped by air and naval power alone.
What was the Truman administration concerned about that was preventing them from getting involved in the Korean conflict?
Soviet reaction

In a grounded-emitter transistor circuit, such as the light-switch circuit shown, as the base voltage rises, the emitter and collector currents rise exponentially. The collector voltage drops because of reduced resistance from collector to emitter. If the voltage difference between the collector and emitter were zero (or near zero), the collector current would be limited only by the load resistance (light bulb) and the supply voltage. This is called saturation because current is flowing from collector to emitter freely. When saturated, the switch is said to be on.
What would happen if the voltage difference from collector and emitter were zero?
the collector current would be limited only by the load resistance (light bulb) and the supply voltage