You shouldn’t use issues of taxation and war to prove that the federal government has increased its powers over the years. The Constitution always has given the federal government the power to make war, so that is not something that has changed over time. Both states and the federal government have the power to tax, and that has not changed. All that said, the federal government’s power has increased relative to the states’ powers.
The federal government’s power has really been growing most strongly since the Great Depression. During that time, President Franklin D. Roosevelt proposed a variety of “New Deal” programs that gave more power to the federal government. For example, they gave the federal government the power to affect the prices of agricultural products and the power to create a national pension system (Social Security). Because of all these programs, the federal government came to have more powers and, more importantly, people started to expect the federal government to do a lot of things to help them.
The next big increase in federal power came in the 1960s. The most important increase in this power came during the Civil Rights Movement. During that time, the federal government took the power to regulate the ways that states treated their citizens. The federal government got the power to ban racial segregation in all public accommodations (Civil Rights Act of 1964). The federal government got the power to tell Southern states how to conduct their elections (Voting Rights Act of 1965). This was also the time when President Johnson’s “Great Society” programs gave the federal government even more powers. For example, it gave the federal government the power to give money to local groups and tell them how to spend it. This bypassed the state governments and allowed the federal government to have more influence within the states.
Since then, some powers have been taken back and given to the states. But for the most part the federal government has continued to take more power for itself. It generally does this by telling states that they will not get federal funding if they do not follow certain rules. The most prominent example of this in recent times is the “No Child Left Behind” law which gave the federal government a great deal of power over educational policy in the states.
In all of these ways, the power of the federal government has increased over time relative to the powers of the state governments.