What is the difference between Kempo and Kenpo?
There is no difference whatsoever - these two terms in roman letters are just one term in Japanese, consisting of two characters: ken, meaning sword or fist, and po, meaning method. When you put these two characters together some Japanese pronounce the "n" as an "m".
I've heard the name of Kempo but nothing else about it.
Given the highly politicised nature of their original applications, it is perhaps not surprising that even today a great deal of secrecy surrounds these crafts, many of which became latterly associated with right wing politics in Japan (something that today is a bit of a non-subject in its own right in Japan). It should be noted however that this latter aspect was very much a feature of what happened after 1868, and not of what went before. The feudal groups with whom Kempo’s precursor arts were originally associated fell largely into the fairly liberal, outwardly looking political camp. Indeed had it not been for the desire of the early Ashikaga Shoguns to establish friendly relations with China Kempo would never have come into existence.
Today there is not really any good reason for some Kempo schools to be overly secretive other than its long established tradition of secrecy. Thus it is very much a matter of secrecy for secrecy's own sake. Rather than evaluating this as a good thing or a bad thing, it is better simply to accept it as a neutral fact, because taking any other position will inevitably restrict ones ability to learn more.
How did Kempo come to be as it is today?
Many Kempo masters agreed that the continued existence of their arts as formal ryuha (schools) after the Meiji Restoration (1868) was inappropriate. Most of Kempo today consists of fragments of traditions that, if they ever were organised ryuha (and many were not, even during the feudal period), were disbanded as such long ago. Furthermore, the past of the crafts that we now call Kempo was not altogether free of shame, and during the feudal period Kempo always had a cross-training type of attitude because of its strong Chinese connection, so Kempo does not fit neatly into the modern Japanese conception of formal, highly organised martial arts schools. Kempo has always had an attitude similar to the modern idea of "absorb what is useful", only qualified with "once you have mastered it ". Thus in Kempo to reject a method as useless one must first master it, then reject it, not just reject it because it doesn't seem to work at first. In general Kempo has huge numbers of methods already, so today there is little incentive to add yet more.
What is the Chinese connection?
Although there are exceptions, in general to be called Kempo a martial craft or martial art must have incorporated precursor arts that either originated in China and were imported into Japan, or else have originated in Japan and subsequently been heavily influenced by Chinese culture.
How effective is Kempo?
For the purposes for which they were originally developed, the Kempo methods were very effective. Today people tend to have a distorted understanding of what martial arts are for compared to what they were actually used for in the past. To criticise Kempo for not being "effective" like a modern martial art would be like criticising a screwdriver for its inability to cook pasta. This is not the purpose for which screwdrivers were invented (i.e. to drive screws), and if you're asking this question you're probably not thinking about Kempo's original applications when you ask it.
Certainly Kempo is virtually useless for self defence and sporting applications in the commonly understood sense, and while an advanced practitioner could potentially use it in this way, a beginner or intermediate student probably could not do so. If Kempo were "really used" in such a situation it would produce undesirable results as it uses weapons, even when apparently "barehand", so against unarmed arts serious injury or death would be likely to result. In former times that (small) part of Kempo which could be considered in any way similar to modern martial arts was concerned primarily with killing rather than with competing, so in the modern age it is wholly inappropriate to use the majority of Kempo’s methods as they were used during the feudal period.
Today Kempo is generally studied out of interest, not for actual use.
Why do some Kempo styles have ryu names?
The original ryuha (formal martial arts schools) that most Kempo styles came from were disbanded, so today when you see a ryu name applied to a Kempo school it is usually a modern re-systemisation of Kempo that has been given a new name. This is also true of the name of our school Kaido Miwa Ryu, which is not the original name of any of the original schools that the arts we practice came from. Modern Kempo practitioners tend to practice cut-down sets of Kempo as the original arts were extensive to the point that it would not be possible for the average person to devote enough practice time to the full systems. Further, Kempo styles were rarely practiced in isolation - several different styles were often practiced by one school.
What is Kaido Miwa Ryu?
Kaido Miwa Ryu is a modern ryuha of Kempo that is a combination of the fundamentals of five different Kempo arts/crafts into one system. None of the five systems is represented in its entirety, but rather those fundamentals that were formerly considered the most important and/or characteristic principles of each of the five arts are included. Even though Kaido Miwa Ryu is a heavily cut down Kempo system it still represents a huge body of methods when compared to most modern martial arts, covering five very different styles of fighting across more than 20 different weapons. As a result Kaido Miwa Ryu Kempo remains a time consuming subject to study, and it is not a good bet for someone wanting to learn self defence in a hurry. It is much more likely to appeal as a matter of interest and a long-term challenge to an already experienced martial artist. That is to say, Kempo makes an interesting study for experienced practitioners of other martial arts styles not because it compliments what they do, but just the opposite - because it is so different.
The phrase "Kaido Miwa Ryu" breaks down into Chinese characters (kanji) as follows: Ka (transform/change/smelt), -i- (will/volition), -do (method, way), Mi (from mitsu meaning three), -wa (ring, segment), Ryu (tradition/school). The three rings refer to the three realms of the Yoshida Shinto cosmology: Takamagahara, Nakatsukuni and Yominokuni.