Throughout history, there have been many significant events which have shaped the way the world is today. As the post from 
My entry for the 100 Year History Challenge is to share and talk about The Standard Time Act of 1918 (also known as the Calder Act) which I feel is significant because a majority of us including myself observe and live our life according to the different time zones established and defined by this.
What is the Calder Act?
This federal law was first established by the US Congress in 1918 to implement Standard time and Daylight saving time in the United States. It authorized the Interstate Commerce Commission to define each time zone. On March 19, 1918 President Woodrow Wilson officially signed into law the Standard Time Act, setting federally mandated time zones across the US. Daylight saving time began on March 31 which meant setting clocks forward 1-hour so that there would be more daylight during the evenings of warmer months and less during the mornings.
Why were timezones established?
According to history, most North American railroads were using their own standard time system which governed their timetables. Because of this, each of the various railroads was publishing conflicting schedules which were based on the local time of their main headquarters. Since the headquarters were located in different geographical locations on different continents, this led to confusing, and often times conflicting schedules due the "differences in their geographical longitudes, which varied by four minutes of time for every degree of longitude - according to wikipedia.org." All of this confusion was resolved when The Standard Time Act was put in place.
Image Source
Not everyone supported this change and according to several articles, there were a number of people who were against the bill, most notably, the American Railway Association.
D.C. Stewart of the American Railway Association presented a dangerous situation with the time change. Stewart was concerned about the risk of accidents on single-track railroads. There were 1,698,818 clocks and watches that would need to be changed on all the railroads. Stewart believed the risk of misinterpretations and mistakes on changing clocks was too high. Senator Frank Kellogg of Minnesota provided a solution that would minimize potential problems for railroads. Kellogg asked Stewart at what point in the day the fewest number of trains were running. Stewart told him two o’clock in the morning, and this became the designated transition time in the bill. This confirmed the transition time in all American DST laws since. [Source]
It is important to note that this was only the first iteration of this law. Over the next several years, it has been amended, changed, and updated due to various factors such as changing geographies, seasons, and local occurrences which required that the timezones and DST be adjusted to hopefully benefit most people. The law also does not require that anyone MUST observe daylight saving time, it just specifies that those who do decide to observe it should do so as an entire city/state and not individually. To date, not all city/states do observe DST.
I hope this has proven to be a learning experience. Before this post, I had not known about the details leading to the establishment of time zones and daylight savings in the United States. I knew there was a lot of controversies surrounding them and that not everyone supported or even liked them, so this was a good opportunity for me to get more familiar with the history behind it. I hope it is the same for you.
Sources for research and reference:
Time zone Wikipedia
Daylight Saving Time: When, Where, and Why?
US Law Full Text
Uniform Time Act - US Department of Transportation